A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

Who is that with a neck and no head, two arms and no hands? What is it?

Find the next number in the series

12, 20, 40, 72, 116, 172 ?

What is always in front of you but can’t be seen?

A bomb exploded in a room full of married couples and no one died. How?

Find the next number in the series below

21 32 54 87 131 ?

You have two buckets of 11 liters and 6 litres.
How can you measure exactly 8 litres?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

I am a prime number.
The double of myself is equal to the square of me.

which number am I?