What month of the year has 28 days?

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

Forwards I am heavy, backward I am not. What am I?

What brings you down but never up?

What numbers should go on the bottom line?
3 6 9 15
8 2 10 12
11 8 19 27
19 10 29 39
? ? ? ?

John is asked to stand behind Jacob and Jacob is asked to stand behind John. Both of them feel confused about it and don't know what to do?

But it is quite possible, do you know how?

Find the next number in the sequence

1, 2, 6, 21, 88, __?

I am never scared but became petrified and can’t live in a house but would die to make one. What am I?

Can you count the number of squares in the figure below?

What has 88 keys?