When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

Can you find out the remainder when 3^300 is divided by 5?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

You have 1023 apples and 10 bags. You have to distribute these apples in these 10 bags in any way you choose. But when I ask for a certain number of apples you have to give them in terms of bags without transferring the apples from other bags. How do you distribute the apples?

What number comes next in the series?

5 15 5 18 5 24 14 20 _

81 x 9 = 801. What must you do to make the this equation true?

Can you count the number of lines in the below picture?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?