Math Riddles

These Math Riddles are based on math concepts and can be solved with a bit of math and logic. These fun riddles can surely give you a tough time.

Pocket Money

You have unlimited supply of 1¢, 5¢, 10¢, 25¢ and 50¢ (penny, nickel, dime, quarter, half-dollar respectively) coins. What is the fewest number of coins required to have an exact change for all possible items that cost from one cent up to and including one dollar in one-cent increments?

Riddle Answer

Mr Tan’s Birthday

Ben and Mark are students of Mr Tan. Mr Tan’s date of birth is on N/M/1970 and both of them know that Mr Tan’s birthday is one of these 10 dates:

4/3/1970  5/3/1970   8/3/1970
4/6/1970  7/6/1970
1/9/1970  5/9/1970
1/12/1970 2/12/1970  8/12/1970 

Mr Tan tells Ben the value of M and tells Mark the value of N. Then Mr Tan asks them: “Do you know when my birthday is?”

Ben says: “I don’t know, but I can be sure that Mark doesn’t know either.”
Mark says: “Initially I don’t know, but now I do.”
Ben says: “Oh, then now I know it too.”

Based on this dialogue and the dates given, can you figure out which is the correct date of Mr Tan’s birthday?

Riddle Answer