GRiN and Solve It

November 7, 2014 at 7:55 pm 4 comments

My boys have been asking to do Math Trivia before bedtime each night, and one of my favorite sites, GRiN: Good Riddles Now, has provided a treasure trove of fun puzzles that they can solve.

Here’s one of them.

There are 100 coins on the floor in a dark room: 90 coins show heads, the other 10 show tails. If you’re not allowed to turn on any lights, how can you divide the coins into two piles so that each pile contains the same number of coins showing tails?

GRiN was started by Justin Zablocki, a math major cum computer scientist who enjoys logic and puzzles. He created GRiN as a way to practice his web development skills and to “improve upon an underdeveloped entertainment category.” (Hear, hear!)

His favorite math joke?

Why does no one talk to π?
He’s irrational and goes on forever.

His favorite riddle?

A murderer is condemned to death. He has to choose between three rooms. The first is ablaze with raging fires, the second is full of assassins with loaded guns, and the third contains lions who haven’t eaten in three years. Which room is safest for him?

Keeping with today’s theme, here’s a math riddle quiz for ya. Enjoy.

  1. How is the moon like a dollar?
  2. A plane with 56 passengers crashes on the border between Canada and the United States. Where do they bury the survivors?
  3. When spelled out, what is the first positive integer that contains the letter a?
  4. In a race of 548 runners, you overtake the last runner. What place are you now in?
  5. The first term of a sequence is a1 = 13. Every term thereafter satisfies a1 ∙ a2 ∙∙∙ ak = k! for k > 1. What is the 31st term of this sequence?
  6. There are four cookies in the cookie jar. You take three of them. How many do you have?
  7. If you remove the first letter, the last letter, and all the letters in between, what do you have left?
  8. What is the next number in the sequence 1, 4, 5, 6, 7, 9, 11, …?
  9. What is the product of all the digits on a telephone dialpad?
  10. If you have 6 apples in one hand and 7 oranges in the other, what do you have?
  11. What has a face and two hands but no arms or legs?
  12. What occurs once in a minute, twice in a moment, but never in a thousand years?
  13. A man has four daughters, and each daughter has a brother. How many children does the man have?


  1. Both have four quarters.
  2. You don’t bury survivors.
  3. One thousand.
  4. Trick question. It’s not possible to overtake the last runner, because you’d have to be behind him, in which case you’d be the last runner.
  5. 31.
  6. Three.
  7. The mailman.
  8. 100. The pattern of numbers are the positive integers that do not have a t in them when spelled out.
  9. 0.
  10. Big hands.
  11. A clock.
  12. The letter m.
  13. 5. One son is a brother to each of the daughters.

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4 Comments Add your own

  • 1. Semane  |  December 2, 2014 at 6:35 am

    The correct answer to 3 is actually: One hundred And one.

    • 2. venneblock  |  December 2, 2014 at 6:55 pm

      Correct pronunciation of 101 is “one-hundred one.” It is incorrect to include and here, since and is only to be used to indicate the decimal point, as in pronouncing 1.23 as “one and twenty-three hundredths.”

  • 3. Semane  |  December 2, 2014 at 6:41 am

    The correct answer for 4 is 548. The race has 548 runners; that is a statement. When you overtake the last runner and assume a position you have entered the race.

    • 4. venneblock  |  December 2, 2014 at 6:58 pm

      I see your point, but It feels like this forms a logical paradox… if you’re one of the 548, then you can’t “enter the race” because you’re already in it; and if you’re not one of the 548, then when you enter the race, it will now have 549 runners, which contradicts the initial statement.


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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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