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

You have two hour glasses one measures 7 minutes and the other measures 4 minutes.
Using these two-hour glasses, you need to measure exactly 9 minutes.

How come?

There are three houses in a straight row. One is red, one is blue, and one is white. The red house is left of the middle. The blue house is right of the middle. Where's the white house?

Solve the rebus riddle in the picture below.

Can you replace the question mark with the correct number in the below table sequence?

A spy was in Canada trying to steal insider information on how to set up new Maple Syrup factories in their country. He was introduced to the operations manager of the biggest factory in Canada. However, the manager was suspicious and decided to test him with a question before he trusted him. So he asked, “What would you be sure to find in the middle of Toronto?” The spy thought fast and came up with an answer for the manager. What was his answer?

What has no start, end, or centre?

I have a mouth but I don't eat.
I have a bank but have no money.
I have a bed but i dont sleep.
I wave but have no hands.

Who Am I ?

This is a famous paradox which has caused a great deal of argument and disbelief from many who cannot accept the correct answer. Four balls are placed in a hat. One is white, one is blue and the other two are red. The bag is shaken and someone draws two balls from the hat. He looks at the two balls and announces that at least one of them is red. What are the chances that the other ball he has drawn out is also red?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?