My Mathematical Magic Show: Index

I’m doing something that I should have done a long time ago: collecting a series of posts into one single post. The links below show the mathematical magic show that I’ll perform from time to time.

Part 1: Introduction.

Part 2a, Part 2b, and Part 2c: The 1089 trick.

Part 3a, Part 3b, and Part 3c: A geometric magic trick.

Part 4a: Part 4b, Part 4c, and Part 4d: A trick using binary numbers.

Part 5a, Part 5b, Part 5c, and Part 5d: A trick using the rule for checking if a number is a multiple of 9.

Part 7: The Fitch-Cheney card trick, which is perhaps the slickest mathematical card trick ever devised.

Part 8a, Part 8b, and Part 8c: A trick using Pascal’s triangle.

Part 6: The Grand Finale.

And, for the sake of completeness, here’s a recent picture of me just before I performed an abbreviated version of this show for UNT’s Preview Day for high school students thinking about enrolling at my university.

magician

 

Engaging students: Solving one-step algebra problems

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Jason Trejo. His topic, from Algebra: solving one-step algebra problems.

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A2) How could you as a teacher create an activity or project that involves this topic?

How can I engage my students with solving for a variable? Off the top of my head, I came up with 3 tried and true surefire ways that would not only further my students understanding but also be a ton of fun for them: Algeblocks with accompanying interactive whiteboard, using a balance and counters, and possibly using snacks (e.g. cookies, chips, candies, etc.)

First things first, the Algeblocks:
algeblocks

Essentially, Algeblocks are made of a variety of cubes and rectangles that represent ones, tens hundreds, thousands, and even the variables x and x2. Although obscured in the picture, the Algeblocks mat in the back represents a balance where the fulcrum is “=” and each end of the balance represent both sides of the equation. There is even a place that represents negative numbers! Using the problem “x+4=8”, students would have 8 green blocks to the left of the fulcrum and 4 green blocks with an x block. Students would then add or take away tiles to solve the equation. As for problems such as “4x=16”, the students would display the problem using the blocks and then group the green blocks with the x’s to find there answer. Now that I think of it, I would essentially do the same thing but use either a real balance with any type of manipulative.

 

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B1) How can this topic be used in you students’ future courses in mathematics or science?

Being able to solve single step algebraic problems is a foundation to algebra in general, correct? This means that this will continue to pop up regardless of what math class (and even science classes like chemistry). There will always be problems given to students where they will need to solve for a variable and the final step of even the most excruciatingly, horrific looking algebra problems is usually adding, subtracting, multiplying, dividing, etc. to get the “x” all alone. In reality, solving an initial value problem (like I currently do in my Differential Equations class) boils down to one step algebraic solutions.

 

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E1) How can technology (YouTube, Khan Academy [khanacademy.org], Vi Hart, Geometers Sketchpad, graphing calculators, etc.) be used to effectively engage students with this topic?

Interestingly enough, I have the perfect example that ties both Khan Academy and the “use of a balance” activity I mentioned earlier. A quick Google search for “one-step equations” gives a link to Khan Academy that allows for a digital balance and you are to solve the equation given with the balance. This would be an amazing tool for teachers to use when they don’t have actual balances for their class or even have their students create a profile on Khan Academy and use it to be able to track extra problems the students can do. Besides Khan Academy, there are even some cheesy yet fun games (like “Equations Pong” off the XP Math website) that would give the students more practice with these equations while feeling like a reward since they are playing a game. Plus, students can go head-to-head in “Equations Pong” and a vast majority of students like to best their friends in anything and everything.

 

References:

Information on Algeblocks: http://www.hand2mind.com/brands/algeblocks

Image of Algeblock Mats: https://cdn.hand2mind.com/productimages/76986_Algeblocks_Mats_BQS-web.jpg

Khan Academy use for subject: https://www.khanacademy.org/math/algebra/solving-linear-equations-and-inequalities/why-of-algebra/e/one_step_equation_intuition

Equations Pong Game: http://www.xpmath.com/forums/arcade.php?do=play&gameid=105

 

Engaging students: Rational and irrational numbers

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Emma Sivado. Her topic, from Algebra: rational and irrational numbers.

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D.1: What interesting things can you say about the people who contributed to the discovery and/or the development of this topic?

The famous story on the first discovery of irrational numbers is one of violence. We all know the Pythagorean theorem, a2+b2=c2 , but what happens if we have a right triangle with height 1 and base 1? The hypotenuse becomes √2. So, √2, what’s the big deal? Well this is where we turn to history for the answer. Hippassus was an ancient greek philosopher who belonged to the Pythagorean school of thought. Now the Pythagorean’s had a saying, “All is number.” What do we think this means? What Pythagoras meant was that everything in the universe had a numerical attribute. For example, one is the number of reason, five is the number of marriage. So one day when Hippassus was playing with the length of the diagonal of the unit square, or the hypotenuse of a right triangle with base 1 and height 1, he discovered the number √2. Hippassus tried to write √2 as a fraction, or rational number, and found it to be impossible. Therefore, √2 is what we call an irrational number. Well this is where the history turns violent. There are numerous stories to explain the death of Hippassus, but all of them point to his ultimate cause of death being the discovery of these irrational numbers. Irrational numbers were so against Pythagoras and the Pythagorean school of thought that they had this man killed!

https://brilliant.org/discussions/thread/discovery-of-irrational-numbers/

http://www.math.tamu.edu/~dallen/history/pythag/pythag.html

 

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B.1: How can this topic be used in your students’ future courses in mathematics and science?

I believe that the irrational number would be a great place to introduce a simple proof. Students will have to do proofs in multiple math classes in the future and to give them an example with an interesting story might be a good place to start. For example, after telling the story of the discovery of irrational numbers ask the students how Hippassus might have proven that this was true; possibly his dying words. Then give them an outline or fill in the black of the proof that √2 is irrational. This example I found on homeschoolmath.net is given in good language and gives good explanations of why everything is done in the order it is:

Let’s suppose √2 is a rational number. Then we can write it √2  = a/b where a, b are whole numbers, b not zero.

We additionally assume that this a/b is simplified to lowest terms, since that can obviously be done with any fraction.

From the equality √2  = a/b it follows that 2 = a2/b2,  or  a2 = 2 · b2.  So the square of a is an even number since it is two times something.

From this we know that a itself is also an even number. Why? Because it can’t be odd; if a itself was odd, then a · a would be odd too. Odd number times odd number is always odd.

Okay, if a itself is an even number, then a is 2 times some other whole number. In symbols, a = 2k where k is this other number. We don’t need to know what k is; it won’t matter. Soon comes the contradiction.

If we substitute a = 2k into the original equation 2 = a2/b2, this is what we get:

2 = (2k)2/b2
2 = 4k2/b2
2*b2 = 4k2
b2 = 2k2

This means that b2 is even, from which follows again that b itself is even. And that is a contradiction!!!

WHY is that a contradiction? Because we started the whole process assuming that a/b was simplified to lowest terms, and now it turns out that a and b both would be even. We ended at a contradiction; thus our original assumption (that √2 is rational) is not correct. Therefore √2 is rational.

 

Obviously this would have to be presented slowly, but I believe that the students could do this and understand it.

http://www.homeschoolmath.net/teaching/proof_square_root_2_irrational.php

 

 

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I would begin by showing the movie clip from Life of Pi when Pi is reciting all the digits of Pi that he knows, or another video of someone reciting a ridiculous number of digits of pi. Then I would ask the students how many digits of Pi there are? When no one could tell me an exact answer I would introduce the irrational number and explain how the decimals will go on forever because this number cannot be written as a fraction like a rational number. At the end of class you could show the kids the Princeton University Pi Day celebration complete with Einstein look alike contests, and pi reciting competitions to win $314.15!

http://www.pidayprinceton.com/

 

References:

 

 

Engaging students: Adding and subtracting a mixture of positive and negative integers

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Diana A’Lyssa Rodriguez. Her topic, from Algebra: adding and subtracting a mixture of positive and negative integers.

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A2. How could you as a teacher create an activity or project that involves your topic?

Algebra tiles are a fun, hands-on way to help students understand how to add or subtract positive and negative integers. Using a mat with a positive and negative side, students can manipulate the 1-tiles. Using the yellow side of the tile for the positive numbers and the red side for the negative numbers, students pair together opposing colors and take those away. The tiles leftover is the answer to the problem. Here is an example:

Step 1:

algebratile1

Step 2:

algebratile2

Step 3:

algebratile3

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B1. How can this topic be used in your students’ future courses in mathematics or science?

Adding and subtracting positive and negative integers is a one of the most crucial foundation skills that students must learn. This concept is demonstrated and needed in almost every math scenario. In its simplest form, students begin to learn this concept around the first grade, 1+1=2. This process is carried over into third grade with multiplication. Then negative numbers are introduced while in sixth grade. Adding and subtracting opposing integers is a continuous concept that consistently builds upon itself, even through algebra, geometry, calculus, or most especially the real world. There is not just one future math course students will use this in; they will use it for the rest of their lives, even if they do not realize it.

 

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E1. How can technology (YouTube, Khan Academy [khanacademy.org], Vi Hart, Geometers Sketchpad, graphing calculators, etc.) be used to effectively engage students with this topic?

YouTube is always a great resource when trying to engage students. The video below explains how positive and negative numbers work when adding and subtracting them.

A lot of the time students struggle with numbers in general, which makes it harder for them to understand why a concept in math works. This video explains how positive and negative numbers work in relation to each other by using characters from Batman instead of numbers. Using the balance and watching the arrow move in either direction, depending on the type of character that was added into or taken out, allows students to see why positive and negative numbers work the way they do. Once they understand this, it makes working with numbers a whole lot easier. This video also does a wonderful job of maintaining the students’ interest by keeping it related to popular culture by incorporating Batman and the Matrix.

 

Engaging students: Ratios and rates of change

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Avery Fortenberry. His topic, from Algebra: ratios and rates of change.

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In this viral YouTube video a man asks his wife the question “If you are traveling 80 miles per hour, how long does it take to travel 80 miles.” The wife overthinks the question and instead of trying to calculate how long it would take using the information of 80 miles per hour and how that they were going to travel one hour, she tries to think of how quick the tires are spinning and estimating the speed using her speed in running. The couple later goes on to talk on the Comedy Central show Tosh.0 where the wife explains the reason she was confused was that she had not slept well the night before and she was stressed with just finishing her finals. This video stresses the importance of making sure people understand that 80 miles per hour means you travel 80 miles in one hour.

 

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The history of a rate of change is interesting when you consider the history of calculus itself. An important concept of calculus is finding derivatives, which is finding the rate of change or slope of a line. Calculus’s discovery was credited to both Isaac Newton and Gottfried Leibniz who both published their work around roughly the same time. This caused a dispute between the two men and they both accused the other of stealing their work. While both contributed much to the world of mathematics, it was many of Leibniz’s concepts of calculus that we still use today such as his notation dy/dx used for derivatives. Despite that Leibniz died poor and dishonored while Newton had a state funeral.

 

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One of my favorite websites is khanacademy.org. This website has helped me from when I was in high school all the way to now it is still helping me understand concepts I may not have fully understood in class. It is a valuable resource to use when teaching about rates of change because there are countless videos over rates of change and slope and derivative that explain in detail all the concepts of it. Also, it has multiple practice problems that help you practice and study for an exam. I even used it for this project to help refresh my memory on rates of change and I was also looking at its word problems to help think of a word problem on my own for the A1 section of this project. Khan Academy also teaches you by reviewing all difficult steps in problems so that you can understand all the concepts.

 

Resources:

https://www.youtube.com/watch?v=Qhm7-LEBznk

http://www.uh.edu/engines/epi1375.htm

www.Khanacademy.org

 

 

 

 

Another poorly written word problem (Part 8)

Textbooks have included the occasional awful problem ever since Pebbles Flintstone and Bamm-Bamm Rubble chiseled their homework on slate tablets while attending Bedrock Elementary. But even with the understanding that there have been children have been doing awful homework problems since the dawn of time (and long before the advent of the Common Core), this one is a doozy.

There’s no sense having a debate about standards for elementary mathematics if textbook publishers can’t construct sentences that can be understood by students (or their parents).

 

badproblem3

On its face, problems 11 and 12 don’t look so bad. For #11, the appropriate inequality is

1400 + 243 + w \le 2000

1643 + w \le 2000

w \le 357

For #12, the inequality is

7 + g \le 15

g \le 8.

These indeed are the answers that the textbook is expecting. However, both answers are wrong because both w and g have to be positive. So the answers should be 0 \le w \le 357 and 0 \le g \le 8. Which would be no big deal — except that these problems appeared before compound inequalities were introduced. (Notice that problems 7 through 10 only contain a single inequality.)

So, in a nutshell, the correct answers for these problems require skills that students have not yet learned at the time that they would attempt these problems.

Another poorly written word problem (Part 7)

Textbooks have included the occasional awful problem ever since Pebbles Flintstone and Bamm-Bamm Rubble chiseled their homework on slate tablets while attending Bedrock Elementary. But even with the understanding that there have been children have been doing awful homework problems since the dawn of time (and long before the advent of the Common Core), this one is a doozy.

There’s no sense having a debate about standards for elementary mathematics if textbook publishers can’t construct sentences that can be understood by students (or their parents).

 

badproblem2

Based only on how the questions are worded, should the answers to #53 and #54 be

5x - 10 < 6x -8 \qquad \hbox{and} \qquad x + 20 < 4x - 1?

Or should they be

5x - 10 < 6(x -8) = 6x - 48 \qquad \hbox{and} \qquad x + 20 < 4(x - 1) = 4x -4?

My answer: I have no idea. An argument could be made for either interpretation. And if a problem can be read two different ways by reasonable readers, then it should never be published in a textbook.

Another poorly written word problem (Part 6)

Textbooks have included the occasional awful problem ever since Pebbles Flintstone and Bamm-Bamm Rubble chiseled their homework on slate tablets while attending Bedrock Elementary. But even with the understanding that there have been children have been doing awful homework problems since the dawn of time (and long before the advent of the Common Core), this one is a doozy.

There’s no sense having a debate about standards for elementary mathematics if textbook publishers can’t construct sentences that can be understood by students (or their parents).

 

badproblem1

This one makes my blood boil. According to its advocates, the whole point of the Common Core standards was to increase the rigor in secondary mathematics. However, this one is SIMPLY WRONG.

The textbook does correctly note that the proper definition of a function is a set of ordered pairs. The “correct” answer, according to the textbook, is answer G — the plotted points do not match the ordered pairs.

However, answer H is also wrong. The textbook would have students believe that order is important when listing the elements of a set. However, order is not important — the domain of \{-3, 1, -1, 3\} is the same as \{-3, -1, 1, 3\} or latex \{3, -3, -1, 1\}$. This is standard mathematical notation — in an ordered pair (or ordered n-tuple), the order is important. For a set, the order is not important.

Specifying that the domain is \{-3,-1,1,3\} and the range is \{2,5,8,11\} does not uniquely determine the function. In fact, there are 24 different functions that have this domain and range (where we distinguish between the range of a function and its codomain).

In other words, in trying to be clever about properly defining a function and showing different representations of a function, the textbook promotes a misconception about sets… which makes me wonder if the textbook’s attempt at trying to be ultra-careful about the definition of a function is really worth it.

Another poorly written word problem (Part 5)

Textbooks have included the occasional awful problem ever since Pebbles Flintstone and Bamm-Bamm Rubble chiseled their homework on slate tablets while attending Bedrock Elementary. But even with the understanding that there have been children have been doing awful homework problems since the dawn of time (and long before the advent of the Common Core), this one is a doozy.

There’s no sense having a debate about standards for elementary mathematics if textbook publishers can’t construct sentences that can be understood by students (or their parents).

 

badproblem4

This one really annoys me. The area is less than 55 square inches, and so the appropriate inequality is

\frac{1}{2} (5)(2x+3) < 55

5(2x+3) < 110

2x + 3 < 22

2x < 19

x < 9.5

However, part (c) asks for the maximum height of the triangle. But there isn’t a maximum possible height. If the height was actually equal to 9.5 inches, then the area would be equal to 55 square inches, which is too big! Also, if any height less than 9.5 is chosen (for the sake of argument, say 9.499), then there is another acceptable height that’s larger (say 9.4995).

Technically, the problem should ask for the greatest upper bound (or supremum) of the height of the triangle, but that’s too much to expect of middle school or high school students learning algebra.

This problem could have been salvaged if it had stated that the area is less than or equal to 55 square inches. However, in its present form, part (c) of this problem is unforgivably awful.