Why Aeroplane windows are round?

From a pack of 52 cards, I placed 4 cards on the table.

I will give you 4 clues about the cards:

Clue 1: Card on left cannot be greater than the card on the right.
Clue 2: Difference between the 1st card and 3rd card is 8.
Clue 3: There is no card of an ace.
Clue 4: There are no face cards (queen, king, jacks).
Clue 5: Difference between the 2nd card and 4th card is 7.

Identify four cards?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

Out of four images which one is the odd one out?

Count the squares in the matchstick puzzle below?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

Can you count the number of matches in the picture below ?

Get total of 120 by using five zeros 0,0,0,0,0 and any one mathematical operator.
Do you ?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?