why number 8549176320 is one of a kind?

Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

When is the top of a mountain similar to a savings account?

One night, a man runs away from home. He turns left and keeps running. After some time he turns left again and keeps running. Later, he turns left one more time and runs back home—but when he gets home, he finds a man in a mask. Who was the man in the mask?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?

You have two buckets of 11 liters and 6 litres.
How can you measure exactly 8 litres?

What is full of holes but still holds water?

If two's company, and three's a crowd, then whats four and five ?

What brings you down but never up?