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!!!

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

Prove that the below maths equation is true.

8 + 8 = 91

What 8 letter word can have a letter taken away and it still makes a word. Take another letter away and it still makes a word. Keep on doing that until you have one letter left. What is the word?

You have 21 jars with you. Out of them, 7 are filled with water, 7 are half-full with water and 7 are empty. How will you distribute the jars among three people such that each one of them gets an equal number of jars and an equal amount of water?

A mules travels the same distance daily.
I noticed that two of his legs travels 10km and the remaining two travels 12km.
Obviously two mules legs cannot be a 2km ahead of the other 2.

The mules is perfectly normal. So how come this be true ?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?