Why Aeroplane windows are round?

I have Rs.50 and I spend it in the way as below.

What is the centre of gravity?

What is the fastest way to double your money?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

A professor thinks of two consecutive numbers between 1 and 10.
'A' knows the 1st number and 'B' knows the second number

A: I do not know your number.
B: Nor do I know your number.
A: Now I know.

What are the four solutions for this?

There is a bag which have 21 blue balls and 23 red balls. You also have 22 red balls outside the bag. Randomly remove two balls from the bag. * If they are of different colors, put the blue one back in the bag. * If they are the same colour, take them out and put a red ball back in the bag. Repeat this until only one ball remains in the bag. What is the color of the sole ball left in the bag ?

Why is it against the law for a man living in Delhi to be buried in Mumbai?

Solve The below Equation:

ALFA + BETA + GAMA = DELTA

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