## Archive for November 7, 2014

### GRiN and Solve It

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.

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.

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

**Answers**

- Both have four quarters.
- You don’t bury survivors.
- One thousand.
- 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. - 31.
- Three.
- The mailman.
- 100. The pattern of numbers are the positive integers that do not have a
*t*in them when spelled out. - 0.
- Big hands.
- A clock.
- The letter
*m*. - 5. One son is a brother to each of the daughters.