Why did the Girl throw the butter out of the window?

They are the five precious gems of an everyday sort and all can be found on a Tennis Court. Who are they?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

My cousin lives in one story house in Antarctica. His house is made the of-of sandstone. what is the color of stairs?

Can you move 2 matchsticks to form four equal sized squares.

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Two Twins Jack and Jill were standing back to back and suddenly they started running in opposite direction for 4 kilometres and then turn to left and run for another 3 kilometres.

what is the distance between the Baggio twins when they stop ?

If 21x = 79x, what is the value of x?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.