What is black when you buy it, red when you use it, and gray when you throw it away?

What do you answer even though it never asks you questions?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

On a windy rainy night , I was driving in my car.
When i reach the bus stand , i see three people waiting for the bus.

1. An old lady who needs an immediate medical attention
2. My Best Friend
3. Girl whom i love from childhood

My car is a two seat, so can you tell me , what i have done in this situation ?

Given that

(78)^9 = 6
And (69)^4 = 11

Can you find out

(99)^2 =?

(Note: This is Logical, not Mathematical)

Name a key which is hardest to turn.

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?