Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What is black when you buy it, red when you use it, and gray when you throw it away?

Can you find a five letter word that is left with only two letters if one is removed?

Solve the mathematical equation in the picture below.

What always comes into a house through the keyhole?

Intelligence Agency need to break the vault but the problem is that they are not able to break the vault.

On the vault, a text is written as:

31 11 33 33 43 45
21 25
31 24 11 31 51 41

To Break the code Intelligence Agency brings a mathematician named Joseph.
Minutes later he deciphers the code.

Whats the code?

who is silent in the parliament?

Which wheel of car does not rotate when you turn your car right?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?