Math Riddles

Are you good at Math? With math + logic, you can solve these tricky Math Riddles. Have fun!

Riddle # 1

Suppose you’re on a game show, and you’re given the choice of three doors: Behind one door is a sports car; behind all of the others are bicycles. You pick a door, say No. 1, and the host, who knows what’s behind the doors, opens another door, say No. 2, revealing a bicycle. He then says to you, “Do you want to pick door No. 3?” Is it to your advantage to switch your choice?

Riddle # 2

If you have an 11 minute and 13 minute hourglass, how can you accurately time 15 minutes?

Riddle # 3

You have a glass of water that looks about half full. How can you tell, only using the glass of water itself, if the glass is half full or not?

The glass is a right cylinder.

Riddle # 4

Two men find an old gold coin and want to have a coin toss with it to decide who gets it. The only problem is the coin is heavier on one side so it comes up heads more than tails. What is a fair way for the men to toss the coin and decide who gets the coin?

Riddle # 5

Why are manholes round instead of square?

Riddle # 6

An ant gets onto one end of a tight rope that is 1 meter long. The ant is traveling at 1 centimeter per second, but the entire rope is being stretched an extra 1 meter (1,000 centimeters) a second (it can be stretched forever).

Will the ant ever reach the other end of the rope?

Riddle # 7

A man in New York City has $10. He spends $6.50 on flowers, and $3 on lunch (hot coffee and a hot dog). He then gets on the subway which will take him 7 stops for 50 cents. But he is forced to get off of the subway just 5 stops away from where he began.

Why is this?

Riddle # 8

How many people do you need to have the odds be in favor (at least 50% chance) of two people having the same birthday?

Riddle # 9

You have a large number of friends coming over and they all get thirsty. Your first friend asks for 1/2 a cup of water. Your second friend asks for 1/4 a cup of water. Your third friend asks for 1/8 a cup of water, etc.

How many cups of water do you need to serve your friends?

Riddle # 10

A smart landscaper is given the task of placing 4 trees so that they are all the same distant away from each other.

How does he do this?