What do you answer even though it never asks you questions?

This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?

Be active and find the killer in the picture Riddle below.

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

In a stable, there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Three men in a cafe order a meal the total cost of which is $15. They each contribute $5. The waiter takes the money to the chef who recognises the three as friends and asks the waiter to return $5 to the men.

The waiter is not only poor at mathematics but dishonest and instead of going to the trouble of splitting the $5 between the three he simply gives them $1 each and pockets the remaining $2 for himself.

Now, each of the men effectively paid $4, the total paid is therefore $12. Add the $2 in the waiters pocket and this comes to $14. Where has the other $1 gone from the original $15?

You see a mathematical expression in the picture. Can you think of a movie that this expression refers to?