This is a classy optical illusion puzzle. What more you can find except bricks in the image below?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

Can you count the number of triangles in the given picture?

Which word is least like the others? Third, fourth, fifth, sixth, seventh, eighth, ninth?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

What does it mean?

What is the centre of gravity?

There is a place where if I stand up straight, I will still be considered sideways.

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

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?