Pearls of Wisdom

Although most educators are unaware that the following quotation was coined by Anna Isabella Thackeray Ritchie, almost all of them have heard it before.

Give a man a fish, feed him for a day.
Teach a man to fish, feed him for a lifetime.

It originally appeared in Mrs. Dymond as, “If you give a man a fish, he is hungry again in an hour. If you teach him to catch a fish, you do him a good turn.”

A modification of this quotation is similarly poignant and more colorful.

Build a man a fire, warm him for a day.
Set a man on fire, warm him for the rest of his life.

There are more direct modifications of the phrase:

  • Teach a man to fish, and you can sell him a ton of accessories.
  • Give a man a fish, and you’ll feed him for a day.
    Teach a man to fish, and he’ll drink beer all day.
  • Give a man a fish, feed him for a day.
    Don’t teach a man to fish, feed yourself.
    He’s a grown man. Fishing’s not that hard, dude.

There are other motivational quotations that I’ve heard throughout my life. One inspired the following image:

Removed BonesA similar pontification has been making its way around the Internet recently, but it gives me pause.

Population Around the Equator

The math of this declaration is highly troubling. Assuming each of the 7 billion people on Earth stood side-by-side and held hands with two other humans, and each of them occupied approximately two feet of width, their entire length would be 2.7 million miles. That’s more than 100 times the distance around the Earth at the equator.

Using that same estimate — two feet of width per person — it would only take about 65 million people to circle the Earth at the equator. So a better version of this joke might be:

If everyone from California and Texas held hands around the equator, a significant portion of them would drown.

The problem with this modification is obvious. There are those who believe that sacrificing all Californians would be justified if it means being rid of all Texans; and there are those who believe that sacrificing all Texans would be justified if it means being rid of all Californians.

I’ll continue to work on a better modification, but I’d love to hear some suggestions from you.

June 15, 2014 at 11:11 am Leave a comment

13 Math Jokes that are PG-13 (or Worse)

Triskaidekaphobia is an abnormal fear of the number 13. If you suffer from this ailment, then you might want to stop reading now.

Today is the only Friday the 13th that will occur in 2014. Which makes it a good day for some trivia questions.

  • Is there at least one Friday the 13th every year? If so, prove it. If not, provide a counterexample.
  • What is the maximum number of times that Friday the 13th can occur in a (calendar) year?
  • What is the average number of times that Friday the 13th occurs in a year?

You can check out my previous post Good Luck on Friday the 13th to find the answers to those questions.

This is also a good day for some off-color math jokes. Then again, is there a bad day for off-color math jokes?

Why is 1 the biggest slut?
It goes into everything.

What has six balls and abuses the poor?
The lottery.

Math is a collection of cheap tricks and dirty jokes.

What do calculus and my penis have in common?
Both are hard for you.

Old statisticians never die.
They just get broken down by age and sex.

Algebraists do it in fields.
Or do they do it in groups?

What do you call an excited quadrilateral?
An erectangle.

What covers the genitalia of a hexahedron?
Cubic hair.

A knight with a 20-inch penis told a wizard that he wanted a smaller penis. The wizard told him to propose marriage to an enchanted princess. He did, and the princess said, “No.” His penis instantly shrunk to 16 inches. Happy with this result, he asked her again. Again she said, “No,” and his penis shrunk to 12 inches. He realized that each time she said, “No,” his penis shrunk by 4 inches. So he asked one last time. “How many times do I have to refuse you?” she asked. “No! No! No!”

How is math like sex?
I don’t get either one.

How is sex like fractions?
It’s improper for the larger one to be on top.

Why did you break up with that math student?
I caught her in bed, wrestling with three unknowns.

13 is the square root of 169. What is the square root of 69?
Ate something.

June 13, 2014 at 1:13 pm Leave a comment

2 Truths and a Lie (Mathematician Version)

Here’s the question that started all of the nonsense that follows:

You come to a fork in the road. One fork leads to the village, the other leads to almost certain death. There are three guards stationed at the fork: two always tell the truth, and one always lies. What one question can you ask to one of the guards to find out which fork leads to the village?

There is a truly logical answer to this question, but my favorite answer is:

Did you know they’re giving away free beer in the village?

and then follow all three of them as they sprint toward the village.

Labyrinth Puzzle - xkcd

A similar question that got me thinking:

A kind but eccentric king has three beautiful daughters. The eldest daughter always tells the truth, the middle daughter always lies, and the youngest daughter will answer any question randomly, either yes or no. To be sure, you would like to marry the one who always tells the truth; but, you are willing to settle for the one who always lies, because at least you’ll always know where you stand. Under no circumstances would you like to marry the crazy one.

The king offers you the hand of one of his daughters in marriage. He allows you to ask one yes/no question of one of the daughters. What question should you ask to ensure that you don’t marry the crazy one?

Variations of this question have been discussed on Straight Dope and xkcd.

And those two questions got me thinking about the icebreaker game Two Truths and a Lie, wherein each person at a social gathering tells two truths and one lie about themselves, and the others have to discern fact from fiction.

So I imagined…

What would happen if the most famous mathematicians in history played Two Truths and A Lie with one another?

The following is what I suspect some of them might say. (The answers follow below.)

Isaac Newton

  1. Newton’s Cannonball is named after one of my thought experiments.
  2. The city of Newton, MA, is not named after me, but Newton Township, OH, is.
  3. The Fig Newton, manufactured by Nabisco, is named after me.

Rene DesCartes

  1. I did not get out of bed most days until 11 o’clock in the morning.
  2. I posited that boiled water freezes more quickly than other water.
  3. I started college at the age of 10.

Abraham de Moivre

  1. I noted that I was sleeping 15 minutes longer each day, and using that arithmetic progression, I predicted that the day I would sleep for 24 hours would be the exact day of my death — and I was correct.
  2. I was unable to garner a university post in England, but I was appointed to a Commission of the Royal Society to determine if Newton or Leibniz was the first to discover the calculus.
  3. I gained great and immediate notoriety for discovering the normal (bell) curve.


  1. My name is a Greek word that means “good glory.”
  2. Abraham Lincoln would often quote me in his speeches.
  3. I proved the infinitude of primes using a proof by contradiction.

Gottfried Wilhelm Leibniz

  1. I discovered the calculus.
  2. I invented the first four-function calculator.
  3. My vast estate was left to my son after my death.

Leonardo Pisano (Fibonacci)

  1. I love rabbits!
  2. I sometimes used the name Bigollo to refer to myself, which means “good-for-nothing traveler.”
  3. The 20th century pianist Liberace created his stage name from a contraction of my book title, Liber Abaci.

Grace Murray Hopper

  1. In 1973, I was the first American and the first woman to be elected a Distinguished Fellow of the British Computer Society.
  2. I invented the computer language COBOL.
  3. I received 36 honorary degrees.

Leonhard Euler

  1. All of my work, now collected in Opera Omnia, contains over 70 volumes.
  2. In 1735, Guillaume De L’Isle and I prepared a map of the Russian Empire.
  3. I was the first to use the notation f(x) for a function, e for the base of natural logs, i for the square root of –1, and π for the ratio of circumference to diameter of a circle.

Diophantus of Alexandria

  1. It is believed that I lived to 84 years of age, based entirely on a problem that appeared in a Greek anthology compiled by Metrodorus.
  2. I was a potato farmer.
  3. I proved that 24n + 7 cannot be expressed as the sum of three squares, for integer values of n.

Evariste Galois

  1. I was home-schooled until age 12.
  2. I was killed in a duel, but history is unsure of the other duelist or the reason for the duel.
  3. I transcribed most of my ideas for what is now called Galois theory the night before the duel.

The third statement from each mathematician was their lie. Below is explication.

Isaac Newton: The Fig Newton is named after the town of Newton, MA, where it was first manufactured.

Rene DesCartes: Actually, he started college at the age of 8.

Abraham de Moivre: In fact, de Moivre’s discovery of the normal curve went almost unnoticed.

Euclid: While many claim that Euclid’s proof of the infinitude of primes uses a proof by contradiction, Michael Hardy and Catherine Woodgold debunk this belief in Mathematical Intelligencer, Vol. 31, No. 4, pp. 44–52. Hardy claims that the proof written by Euclid is simpler and more elegant than the proof often attributed to him.

Gottfried Wilhelm Leibniz: He had neither a vast estate nor a son. He was never married, and he died nearly destitute.

Leonardo Pisano (Fibonacci): Though it would be a great piece of trivia, Liberace’s name had nothing to do with Fibonacci. Liberace was a family name; he was born Władziu Valentino Liberace, but he used only his last name on stage.

Grace Murray Hopper: She received at least 37 honorary degrees, perhaps more.

Leonhard Euler: Euler deserves credit for a lot of things, but he does not deserve credit as the first to use π. That distinction belongs to William Jones who used the symbol in 1706.

Diophantus of Alexandria: Though he claimed that 24n + 7 cannot be expressed as the sum of three squares, he had no proof of it.

Evariste Galois: The myth that he basically transcribed Galois theory the night before his death is greatly exaggerated. He wrote a lot that evening, but he published three papers in the year before his death, which collectively contained most of his work.

May 28, 2014 at 9:02 am Leave a comment

Peanut Distribution

When we recently bought honey roasted peanuts at the grocery store, Eli speculated that there were 215 peanuts in the jar.

“I think there are less,” Alex said. “My guess is 214.”Honey Roasted Peanuts

“Okay, so now we have to count them,” Eli said.

“No,” I said, explaining that I didn’t want them touching food that others would be eating. I then showed them the back of the jar, which said that one serving contained about 39 pieces and the whole jar contained about 16 servings. They knew that 39 × 16 would approximate the number of pieces, and they estimated that the jar contained 40 × 15 = 600 pieces.

But then they wanted the actual value, and I wondered how we could use the estimate to find the exact product. More importantly, I wondered if it was possible to find an algorithm that would allow an easily calculated estimate to be converted to the exact value with some minor corrections.

My sons’ estimate used one more than the larger factor and one less than the smaller factor; that is, they found (m + 1) × (n – 1) to estimate the value of mn. A little algebra should help to help to provide some insight.

The product had a value of 600, so further refinement led to:

\begin{aligned}  (m + 1)(n - 1) &= 40 \times 15 \\  mn - m + n - 1 &= 600 \\  mn &= 601 + m - n  \end{aligned}

This led to an algorithm:

  1. Find an estimate with nice numbers.
  2. Add 1.
  3. Add the larger factor.
  4. Subtract the smaller factor.

This gives 600 + 1 + 39 – 16 = 624. And sure enough, 39 × 16 = 624.

This method works any time you want to find the exact value of a product when the larger factor is one more than a nice number and the smaller factor is one less than a nice number. Just estimate with the nice numbers, then follow the steps. The method can be modified if the larger factor is one less than a nice number and the smaller factor is one more than a nice number:

  1. Find the estimate.
  2. Add 1.
  3. Subtract the larger factor.
  4. Add the smaller factor.

So if you want to find the product 41 × 14, then the larger factor is one more than 40 and the smaller factor is one less than 15. The estimate is again 40 × 15 = 600.

Then 600 + 1 – 41 + 14 = 574. And sure enough, 41 × 14 = 574.

The same idea can be extended to numbers that aren’t the same distance from nice numbers. But that’s not the point. The intent was not to find general methods for every combination; instead, the hope was to use an easily calculated estimate as the basis for an exact calculation. I’m not sure this method completely succeeds, but it was fun for an afternoon of mental gymnastics.

May 11, 2014 at 11:40 pm Leave a comment

Cows and Probability

Bert Tolkamp et al. were awarded an Ig Nobel Prize for answering a question that has long been on the minds of readers of this blog, and likely on the minds of the populace at large:

Are cows more likely to lie down the longer they stand?

I mean, seriously, how many nights have you lain awake pondering that question?

Their research revealed two startling facts:

  • The longer a cow has been lying down, the more likely that the cow will soon stand up.
  • Once a cow stands up, it’s impossible to predict how long until that cow lies down again.


I, for one, will rest easier knowing that these questions have finally been answered.

If you suffer from insomnia, the full article may be more valuable than Unisom, chamomile tea, or counting sheep.

You have to wonder if the researchers used a cow-culator to calculate the probabilities. Or perhaps that had to rely on techniques from advanced cow-culus.

Why do milking stools only have three legs?
Because the cow has the udder!

What do Greek cows say?

What do you call a male cow that swallows a hand grenade?

What do you call the same cow 5 seconds later?

Here are some other mathy cow jokes I’ve posted in the past.

May 3, 2014 at 10:39 pm Leave a comment

So Teach Your Children Math…

According to CareerCast, three of the four best jobs in 2014 are in STEM fields: mathematician, statistician, and actuary. And the other — tenured university professor — might very well be a STEM career, too.

The worst job? Lumberjack, with a median annual salary of $24,000, a bad work environment, high stress, and a dismal hiring outlook.

Even though they’re on opposite ends of the best job spectrum, math folks and loggers have a lot in common. Both appreciate natural logs.

I learned this at, which has a few interesting tidbits. But not enough to keep me interested, so I logged out.

And we all know that the grass is always greener, which is why some mathematicians opt for a life in the forest…

A math professor had enough of academic life, so he decided to become a lumberjack. He was hired by a logging firm, and he was told that he’d need to cut down 50 trees a day. On his first day, he was handed a chainsaw, and he went into the forest. When he returned to the office at the end of the first day, the foreman asked him, “So, how many trees did you cut down today?”

“Six,” replied the mathematician.

“That’s not enough,” said the foreman. “You’ll have to do better. Get up earlier tomorrow.” So he did, and again he went into the forest with a chainsaw. He returned at the end of the day, sweaty and exhausted. “How many’d you get today?” the foreman asked.

“Twelve,” replied the mathematician.

So the next day, the foreman went out to the forest with the mathematician. He started the chainsaw, started to cut, and explained to the mathematician what he was doing. When he finished, he said, “And that’s how you cut down a tree. Any questions?”

“Yeah,” said the mathematician. “What the hell was all that noise coming from the chainsaw?”

April 26, 2014 at 10:29 am Leave a comment

Games My Brain Plays

The French Quarter Festival and the NCTM Annual Meeting took place concurrently in New Orleans last week. So following five days of spectacular conversations and presentations at the conference, I headed to the festival for stage after stage of live music.

I sat on the lawn in Woldenberg Park, and the woman next to me was movin’ and groovin’ to the sounds of The Dixie Cups. I introduced myself, and she replied, “Hi, I’m Rhonda.” And the first thought that went through my head was…

Hard-on is an anagram of Rhonda.

What the hell’s the matter with me?

If you’re looking for a silver lining here — and believe me, I am — it’s that there are no other one-word anagrams of Rhonda. So at least I didn’t ignore a more socially appropriate anagram and jump straight into the blue.

But you have to wonder why that happened at all, instead of just accepting her name at face value and politely, automatically responding, “Nice to meet you.”

My mind has played games for as long as I can remember, often without my consent. The following are a list of some of them:

  • Playing License Plate Algebra with the letters and digits on a license plate. For instance, if a Pennsylvania license plate has TFT to the left of the keystone and 567 to the right, and the keystone is then replaced by an equal sign, and some simplifying is done, this reduces to T2F = 567, and I search for order pairs (T, F) that make that equation true.
  • Riding in a car, I’ll pick a speck of dirt on the window and pretend that it’s a laser/bomb/WMD. As I ride along, anything that the speck appears to touch while I look out the window is destroyed instantly.
  • Sometimes, I’ll try to figure out what I’d do if a normal, daily event turned into a life-threatening situation (like this).
  • Eating M&M’s two-by-two, one for each side of my mouth. (See my ruminations about a quest to find The Perfect Pack.)
  • Having to step on an equal number of cracks with each foot, when walking on the sidewalk through our neighborhood.
  • While playing basketball and other sports, getting fixated on a word — say, precise — and when I’m not dribbling or shooting, I’m finding anagrams of the word in my head, or I’ll start to combine pieces of letters — for instance, a c and an i without its dot could be used to form an a — so now I try to make anagrams of p, r, e, a, s, and e. And sure enough, I’ll stumble onto serape. But that’s not good enough. I’ll then return to precise, combine the r and i to make an n, and now I’ll look for anagrams of p, n, e, c, s, and e. There are none, so I’ll spend the rest of the game in a futile mental search. And two seconds after I convince myself that there are none to be found, the buzzer sounds, and I realize our basketball team has suffered its seventh straight double-digit loss. The defeat wasn’t entirely my fault, but my distractedness surely didn’t help matters, either.

What stupid games does your mind play?

April 21, 2014 at 4:27 pm Leave a comment

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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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