What is the word or phrase?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

That attorney is my brother, testified the accountant.

But the attorney testified he didn't have a brother.

Who is lying?

You need to climb ten stairs. At every stair, you can either take one step up or you can jump two steps up.

In how many different ways you can climb 10 stairs?

Six glasses are in a row. The first three are filled with milk and the last three are empty. By moving only one glass, can you arrange them so that the full and the empty glasses alternate?

Can you find the key in the picture below?

Replace the question mark with the correct number below.

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

Paul's height is six feet, he's an assistant at a butcher's shop and wears size 9 shoes. What does he weigh?

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