Why Aeroplane windows are round?

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

Decode the below four famous ciphers:

8P of the SS
1M of the E
1S of the SS
60M in 1H

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

How many letters are in the alphabet?

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

A car meter reading shows 72927 miles a palindromic number.
what is the minimum number of miles you would need to travel to see another palindromic number on the car meter reading?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

There is an exact a week gap between Christmas and New Year. Hence, It is obvious that the new year that comes right after Christmas comes on the same day of the week.

A Strange thing happened in the Year 1777. Christmas occurs on Wednesday and New Year on Monday. How is that possible?

I am something people love or hate. I change peoples appearances and thoughts. If a person takes care of them self I will go up even higher. To some people I will fool them. To others I am a mystery. Some people might want to try and hide me but I will show. No matter how hard people try I will Never go down. What am I?