Math Riddles
Number and mathematical puzzles that require calculation.
The Brick Problem
A brick weighs 3 pounds plus half its weight. How much does the brick weigh?
Answer: 6 pounds
The Basketball Dilemma
A basketball player scores 18 points in a game. All of his shots were either 2-pointers or 3-pointers. He scored exactly twice as many 2-pointers as 3-pointers. How many 2-pointers did he score?
Answer: 6 two-pointers and 3 three-pointers
The 100 Doors
There are 100 closed doors in a row, numbered 1 to 100. A person walks by each door, opening every door. A second person walks by each door, closing every second door (doors 2, 4, 6, …). A third person walks by, toggling every third door (closing open doors, opening closed doors). This continues for 100 people. After all 100 people have walked by, which doors are open?
Answer: Doors whose numbers are perfect squares (1, 4, 9, 16, 25, 36, 49, 64, 81, 100)
The Penny Riddle
A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?
Answer: 4 sisters and 3 brothers
The Clock Hands Riddle
How many times a day do the hands of a clock overlap?
Answer: 22 times (every 65.5 minutes except at 12 o'clock when they're already aligned)
The Train Tunnel Riddle
Two trains enter a tunnel 200 miles long. Train A travels at 70 mph, Train B at 50 mph. How long after they enter will they meet?
Answer: 1 hour 40 minutes
The Strawberry Patch
If 5 cats can catch 5 mice in 5 minutes, how many cats would be needed to catch 100 mice in 100 minutes?
Answer: 5 cats (the ratio remains the same)
The Counting Puzzle
How many months have 28 days?
Answer: All 12 months have at least 28 days
The Weight Puzzle
Which is heavier: a pound of feathers or a pound of rocks?
Answer: They weigh exactly the same - a pound is a pound
The Mathematical Mystery
If you multiply me by any number, the sum of the digits in the result will always be 9. What number am I?
Answer: 9