What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

A man dies of old age on his 25 birthday. How is this possible?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

I shave every day, but my beard stays the same. What am I?

Why is it very easy to weigh a fish?

Six glasses are in a row. The first three are filled with milk and the last three are empty. By moving only one glass, can you arrange them so that the full and the empty glasses alternate?

I look at you, you look at me, I raise my right, you raise your left. What am I?