Posts tagged ‘math’

Stick Figure Math

I’ll never forget the first time I saw the pattern

1, 2, 4, 8, 16, __

and was dumbfounded to learn that the missing value was 31, not 32, because the pattern was not meant to represent the powers of 2, but rather, the number of pieces into which a circle is divided if n points on its circumference are joined by chords. Known as Moser’s circle problem, it represents the inherent danger in making assumptions from a limited set of data.

Last night, my sons told me about the following problem, which they encountered on a recent math competition:

Stick Figure Problem

What number should replace the question mark?

Well, what say you? What number do you think should appear in the middle stick figure’s head?

Hold on, let me give you a hint. This problem appeared on a multiple-choice test, and these were the answer choices:

  1. 3
  2. 6
  3. 9
  4. 12

Now that you know one of those four numbers is supposed to be correct, does that change your answer? If you thought about it in the same way that the test designers intended it, then seeing the choices probably didn’t change your answer. But if you didn’t think about it that way and you put a little more effort into it, and you came up with something a bit more complicated — like I did — well, then, the answer choices may have thrown you for a loop, too, and made you slap your head and say, “WTF?”

For me, it was Moser’s circle problem all over again.

So, here’s where I need your help: I’d like to identify various patterns that could make any of those answers seem reasonable.

In addition, I’d also love to find a few other patterns that could make some answers other than the four given choices seem reasonable.

For instance, if the numbers in the limbs are a, b, c, and d, like this…

Stick Figure Variables

then the formula 8a – 4d gives 8 for the first and third figures’ heads and yields 8 × 6 – 4 × 9 = 12 as the answer, which happens to be one of the four answer choices.

Oh, wait… you’d don’t like that I didn’t use all four variables? Okay, that’s fair. So how about this instead: ‑3a + b + c – 2d, which also gives ‑3 × 6 + 7 + 5 + 2 × 9 = 12.

Willing to help? Post your pattern(s) in the comments.

[UPDATE (3/9/18): I sent a note to the contest organizers about this problem, and I got the following response this afternoon: “Thanks for your overall evaluation comments on [our] problems, and specifically for your input on the Stick Figure Problem. After careful consideration, we decided to give credit to every student for this question. Therefore, scores will be adjusted automatically.”]


March 5, 2018 at 7:40 am 2 comments

2017 KenKen International Championship

If you like puzzles and ping pong, then Pleasantville, NY, was the place to be on December 17.

More than 200 Kenthusiasts — people who love KenKen puzzles — descended on Will Shortz’s Westchester Table Tennis Center for the 2017 KenKen International Championship (or the KKIC, for short). Participants followed 1.5 hours of solving KenKen puzzles with a pizza party and several hours of table tennis.

KenKen Logo

The competition consisted of three rounds, with the three puzzles in each round slightly larger and more difficult than those from the previous round. Consequently, competitors were given 15, 18, and 20 minutes to complete the puzzles in the first, second, and third rounds, respectively.

Competitors earned 1,000 points for each completely correct puzzle, and 0 points for an incomplete or incorrect puzzle. In addition, a bonus of 5 points was earned for every 10 seconds in which a puzzle was turned in before time was called. So, let’s say you got two of the three puzzles correct and handed in your answers with 30 seconds remaining in the round; then, your score for that round would be

2 \times 1000 + \frac{30}{10} \times 5 = \bf{2{,}015}

The leader after the written portion was John Gilling, a data scientist from Brooklyn, whose total score was 10,195. And if you’ve been paying attention, then you know what that means — Gilling earned 9,000 points for completing all of the puzzles correctly, so his time bonus was 1,195 points… which is the amount you’d earn for turning in the puzzles 2,390 seconds (combined) before time was called. The implication? Gilling solved all 9 puzzles from the written rounds — which contained a mix of puzzles from size 5 × 5 to 8 × 8 — in just over 13 minutes.


As a result, Gilling, the defending champion, earned a spot in the Championship Round against Tess Mandell, a math teacher from Boston; Ellie Grueskin, a high school senior at The Hackley School; and Michael Holman, a technology consultant. In the final round, each of them attempted a challenging 9 × 9 puzzle, which was displayed on an easel for the crowd to see. Solving a challenging 9 × 9 is tough enough; having to do it as 200 kenthusiasts follow your every move is even tougher.

So, how’d they do? See for yourself…

When the dust settled, Gilling had successfully defended his title. For his efforts, he received a check for $500. But more importantly, he retained bragging rights for one more year.

John Gilling - 2017 KKIC

John Gilling and his winning KenKen board at the 2017 KKIC

If you think you’ve got what it takes to compete with the best KenKen solvers, try your hand at the 9 × 9 puzzle that was used in the final round. In the video above, you saw how fast Gilling solved it to win the gold. But even the slowest of the four final-round participants finished in under 15 minutes.

Again, wow.

Finally, I’d be failing as a father if I didn’t mention that my sons Alex and Eli competed in the Delta (age 10 and under) division. Though bested by Aritro Chatterjee, a brilliant young man who earned a trip to the 2017 KKIC by winning the UAE KenKen Championship, Eli took the silver, and Alex brought home the bronze. They’re shown in the photos below with Bob Fuhrer, the president of Nextoy, LLC, the KenKen company and host of the KKIC.

Eli and Bob Fuhrer - KKIC    Alex and Bob Fuhrer - KKIC


For more KenKen puzzles, check out, or see my series of posts, A Week of KenKen.

December 26, 2017 at 9:10 am 2 comments

Number Challenge from Will Shortz and NPR

Typically, the NPR Sunday Puzzle involves a word-based challenge, but this week’s challenge was a number puzzle.

[This challenge] comes from Zack Guido, who’s the author of the book Of Course! The Greatest Collection of Riddles & Brain Teasers for Expanding Your Mind. Write down the equation

65 – 43 = 21

You’ll notice that this is not correct. 65 minus 43 equals 22, not 21. The object is to move exactly two of the digits to create a correct equation. There is no trick in the puzzle’s wording. In the answer, the minus and equal signs do not move.

Seemed like an appropriate one to share with the MJ4MF audience. Enjoy!

October 18, 2017 at 8:07 am 2 comments

The Remote Associates (RAT) and Close Associates (CAT) Tests

The Remote Associates Test (RAT) is a test used to determine a person’s creative potential. When given a collection of three seemingly unrelated words, subjects are asked to supply a fourth word that is somehow related to each of the three stimulus words. For example, if you were given the words cottage, swiss, and cake, you’d answer cheese, because when combined with the three stimuli, you get cottage cheese, swiss cheese, and cheesecake.

To try your hand at one of these tests, you can head to, or you can just keep on reading.

The verdict is out as to whether a high score on the RAT actually means you’re more creative. But what’s not in doubt is how much I love to solve, and to create, these items. It’s a good game for long car rides, and my wife, sons, and I can amuse ourselves for hours by creating and sharing them with one another.

For your enjoyment, I present the following mathematical RAT test: The fourth word related to the three stimulus words in each set is a common math term. Enjoy!

  1. attack / acute / fish
  2. inner / around / full
  3. phone / one / mixed
  4. powers / rotational / point
  5. up / on / hot
  6. tipping / blank / selling
  7. even / duck / couple
  8. black / Bermuda / love
  9. inkhorn / limits / short
  10. sub / hour / tolerance
  11. world / television / infinite
  12. ball / camp / data
  13. Dracula / head / sheep
  14. field / dead / stage
  15. town / off / meal
  16. air / hydro / geometry
  17. common / X / fudge
  18. key / bodily / dis
  19. disaster / 51 / grey
  20. ball / S / hairpin

The Close Associates Test (CAT) is a similar, yet completely fictitious, test that I just made up. Each item on a CAT test contains three words which do not appear to be unrelated in the least; in fact, they are so closely related that finding the fourth word they have in common is somewhat trivial. The following mathematical CAT test will not measure your creativity, though it might reasonably determine the depth of your mathematical vocabulary. Good luck!

  1. acute / obtuse / right
  2. scalene / equilateral / isosceles
  3. sine / logistic / regression
  4. real / irrational / whole
  5. proper / improper / reduced
  6. convergent / infinite / divergent
  7. in / circum / ortho
  8. Pythagorean / De Moivre’s / Ramsey’s
  9. exponential / differential / Diophantine
  10. convex / concave / regular
  11. golden / common / test
  12. square / cube / rational

RAT Answers:

  1. angle
  2. circle
  3. number
  4. axis
  5. line
  6. point
  7. odd
  8. triangle
  9. term
  10. zero
  11. series
  12. base
  13. count
  14. center
  15. square
  16. plane
  17. factor
  18. function
  19. area
  20. curve

CAT Answers:

  1. angle
  2. triangle
  3. curve
  4. number
  5. fraction
  6. series
  7. center
  8. theorem
  9. equation
  10. polygon
  11. ratio
  12. root

Feel free to submit more triples for the RAT or CAT test in the comments.

September 6, 2017 at 7:24 am Leave a comment


Today is a glorious day!

The date is 8/15/17, which is mathematically significant because those three numbers represent a Pythagorean triple:

8^2 + 15^2 = 17^2

But August 15 has also been historically important:

But as of today, August 15 has one more reason to brag: It’s the official publication date of a bestseller-to-be…

Like its predecessor, this second volume of math humor contains over 400 jokes. Faithful readers of this blog may have seen a few of them before, but most are new. And if you own a copy of the original Math Jokes 4 Mathy Folks, well, fear not — you won’t see any repeats.

What kind of amazing material will you find on the pages of More Jokes 4 Mathy Folks? There are jokes about school…

An excited son says, “I got 100% in math class today!”

“That’s great!” his mom replies. “On what?”

The son says, “50% on my homework, and 50% on my quiz!”

There are jokes about mathematical professions…

An actuary, an underwriter, and an insurance salesperson are riding in a car. The salesperson has his foot on the gas, the underwriter has her foot on the brake, and the actuary is looking out the back window telling them where to go.

There are Tom Swifties…

“13/6 is a fraction,” said Tom improperly.

And, of course, there are pure math jokes to amuse your inner geek…

You know you’re a mathematician if you’ve ever wondered how Euler pronounced Euclid.

Hungry for more? Sorry, you’ll have to buy a copy to sate that craving.

To purchase a copy for yourself or for the math geeks in your life, visit Amazon, where MoreJ4MF is already getting rave reviews:

More Jokes 4 Mathy Folks Amazon Review

For quantity discounts, visit Robert D. Reed Publishers.

August 15, 2017 at 11:45 am Leave a comment

Just Sayin’

Heidi Lang is one of the amazing teachers at Thomas Jefferson Elementary School. When she’s not challenging my sons with interesting puzzles and problems, she’s entertaining them with jokes that make them think. On her classroom door is a sign titled Just Sayin’, under which hangs a variety of puns. Here’s one of them:

Last night, I was wondering why I couldn’t see the sun. Then it dawned on me.

That reminds me of one of my favorite jokes:

I wondered why the baseball kept getting larger. Then it hit me.

Occasionally, one of her puns has a mathematical twist:

Did you know they won’t be making yardsticks any longer?

And this is one of her mathematical puns, though I’ve modified it a bit:

When he picked up a 20‑pound rock and threw it 5,280 feet, well, that was a real milestone.

I so enjoy reading Ms. Lang’s Just Sayin’ puns that I decided to create some of my own. I suspect I’ll be able to hear you groan…

  • He put 3 feet of bouillon in the stockyard.
  • When the NFL coach went to the bank, he got his quarterback.
  • She put 16 ounces of poodle in the dog pound.
  • The accountant thought the pennies were guilty. But how many mills are innocent?
  • His wife felt bad when she hit him in the ass with 2⅓ gallons of water, so she gave him a peck on the cheek.
  • Does she know that there are 12 eggs in a carton? Sadly, she dozen.
  • When his daughter missed the first 1/180 of the circle, he gave her the third degree.
  • She caught a fish that weighed 4 ounces and measured 475 nm on the visible spectrum. It was a blue gill.
  • When Rod goes to the lake, he uses a stick that is 16.5 feet long. He calls it his fishing rod.
  • What is a New York minute times a New York minute? Times Square.
  • I wanted to dance after drinking 31 gallons of Budweiser, so I asked the band to play the beer barrel polka.
  • The algebra teacher was surprised by the mass when she tried to weigh the ball: b ounces.

And because this post would feel incomplete without it, here’s probably the most famous joke of this ilk:

  • In London, a pound of hamburger weighs about a pound.

August 1, 2017 at 6:34 am Leave a comment

Our Library’s Summer Math Contest

Every summer, our local library runs a contest called The Great Big Brain Game. Young patrons who solve all of the weekly puzzles receive a prize. The second puzzle for Summer 2017 looked like a typical math competition problem:

Last weekend, the weather was perfect, so you decided to go to Cherry Hill Park. When you got there, you saw that half of Falls Church was at the park, too! In addition to all the people on the playground, there were a total of 13 kids riding bicycles and tricycles. If the total number of wheels was 30, how many tricycles were there?


A tricycle has 3 wheels. (Duh.)

First, some comments about the problem.

  1. I dislike using “you” in math problems. I believe it’s a turn-off to students who can’t see themselves in the situation described. There are enough reasons that kids don’t like math. Why give them another reason to shut down by telling them that they went somewhere they didn’t want to go or that they did something they didn’t want to do?
  2. Word problems are not real-world just because they use a local context, and this one is no exception. This problem attempts to show an application for a system of linear equations, but true real-world problems don’t have all the information neatly packaged like this.
  3. Wouldn’t the person posing this problem already have access to the information they seek? That is, if she counted the number of kids riding bikes and the total number of wheels, couldn’t she have just counted the number of bicycles and tricycles instead? It has always struck me as strange when the (implied) narrator of a math problem wants you to figure out something they already know.

All that said, this was meant to be a fun puzzle for a summer contest, and I don’t mean to scold the library. I don’t know that I’d use this puzzle in a classroom — at least, not presented exactly like this — but I love that kids in my town have an opportunity to do some math in June, July, and August.

Now, I’ll offer some comments on the solution. In particular, the solution provided by the library was different than the method used by one of my sons. Here’s what the library did:

Imagine that all 13 kids were on bicycles with 2 wheels. That would be a total of 26 wheels. But since 30 wheels are needed, there are 4 extra wheels. If you add each of those extra wheels to a bicycle, that’ll create 4 tricycles, leaving 9 bicycles. So, there must have been 4 tricycles at Cherry Hill Park.

And here’s what my son did:

2017 Brain Game Puzzle 2

If you can’t see what he wrote, he created a system of two equations and then solved it:

2a + 3b = 30
a + b = 13

a + 2b = 17
13 – b + 2b = 17
b = 4

2a + 12 = 30
2a = 18
a = 9

That’s all well and good. In fact, it’s perfect if you want to assess my son’s ability to translate a problem and solve a system of equations. But I have to admit, I was a little disappointed. What bums me out is that he went straight to a symbolic algorithm instead of considering alternatives.

I think I know the reason for this. This past year, my son was in a pull-out math program, in which he studied math with someone other than his regular classroom teacher. In this special class, the teacher focused on preparing him to take Algebra II in sixth grade when he enters middle school. Consequently, students in the pull-out class spent the past year learning basic algebra. My fear is that they focused almost exclusively on symbolic manipulation and, as my former boss liked to say, “Algebra teachers are too symbol-minded.”

A key trait of effective problem solvers is flexibility. That type of flexibility comes from solving many problems and filling your toolbox with a variety of strategies. My worry — and this isn’t just a concern for my son, but for every math student in the country — is that students learn algorithms at the expense of more useful problem-solving heuristics. What happens when my son is presented with a problem that can’t be translated into a system of linear equations? Will he know what to do when he doesn’t know what to do?

The previous pull-out teacher said that when she presented my sons with problems that they didn’t know how to solve, their eyes would light up. They liked the challenge of doing something they hadn’t done before. I’m hopeful that this enthusiasm isn’t lost as they proceed to higher levels of mathematics.

July 14, 2017 at 7:00 am 2 comments

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About MJ4MF

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

MJ4MF (offline version)

Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.

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