A word I know has six letters it contains, remove one letter and 12 remain. What is it?

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 ?

Here is what you have to do. You have to throw a ball as hard as you can but it must return back to you even if it does not bounce at anything. Also, you have nothing attached to the ball. There is no one on the other end to catch that ball and throw it back at you.

How will you do it?

I have two sand hourglasses:
1. A 7 minute one and
2. An 11-minute one.

Using just these 2 sand hourglasses, how can I measure time as 15 minutes?

Different lights make me strange by changing me into different sizes. What am I?

Using eight eights and addition only, can you make 1000?

What is the next number in this matchsticks series riddle?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

There are forty elephants and they have forty-fore heads. How can this be possible?

What Adam and Eve do not have but the rest of the people have?