What is more useful when it is broken?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

Here is a mathematical expression that also secretly tells a movie name. What movie is that?

Two-person want to cross a river. Only one boat is present on the riverside that can carry only one person at a time.

However, they still manage to cross the river. How is it possible?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

Which flower has two lips?

What has one eye, but can’t see?

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

Today is John's birthday.
A year ago, John had five candles and he lit all the candles except the one at the last.
Now he is going to light all the candles.

How old is John Today?

(He is not five today.....)

Transform the word THINK into BRAIN while changing only one letter at a time in a manner that each of the word in the process is a real word!!!