What's the only room from which no one can enter or leave

Why do people go to bed?

Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?

A brand new Mobile Phone was on sale at 20% as a promotional offer. By what per cent must the Mobile price be increased to sell it at the original price again?

Can you count the number of squares in the figure below?

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

Move three sticks of the spiral below to form a square.

If an electric train is travelling south, then which way is the smoke going?

A frog is at the bottom of a 30-meter well. Each day he summons enough energy for one 3-meter leap up the well. Exhausted, he then hangs there for the rest of the day. At night, while he is asleep, he slips 2 meters backwards. How many days does it take him to escape from the well?

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?