Which number should replace the question mark?

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

An artist while painting a scenic beauty, decides to paint three layers of blue colour on the sky.

Which layer will go on the first?

How many letters are in the alphabet?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

It begins where the time ends.
Its second is an expression of surprise.
Its third is a question.
Its fourth is urinate.
It ends with a drink.

Which country it is?

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

John buys rice at Rs.60/kg from Britain and then sells them at Rs.5/kg in India. As a result of this, he becomes a millionaire. How come?