What is always in front of you but can’t be seen?

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 ?

How many sides does a circle have?

I have feet, but no legs. Which animal Am I?

Find the combined weight of the Cat, Dog and Rabbit in the given picture.

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

In a mathematical quiz, you are asked the following question:

Use three 9s in a mathematical expression without dividing or multiplying to form the number one.

Can you answer the question?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

What number do you get when you multiply all of the numbers on a telephone's number pad?