Why Aeroplane windows are round?

Can you name four days which start with the letter 'T'?

Replace the question mark with the number below given a simple math problem.

A beggar on the street can make one cigarette out of every 6 cigarette butts he finds. After one whole day of searching and checking public ashtrays the beggar finds a total of 72 cigarette butts. How many cigarettes can he make and smoke from the butts he found?

There is one thing that goes round the house and also inside the house but never even share a brief touch. What is it?

If six children and two dogs were under an umbrella, how come none of them got wet?

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

Solve the puzzle by telling what does below picture means.

What do you get if you add 2 to 100 four times?

I am the fastest animal but cannot climb the tree. What am I?