It has five wheels, though often think four, You cannot use it without that one more, You can put things in it, you can strap things on top, You can't find it in the market, but you can still go shop. What is it?

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

What is harder to catch the faster you run?

What word does this rebus represent?

meta meta
meta meta

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

You can take four of the five letters out of this word, but the pronunciation never changes. What is the word?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

A doctor and a boy were fishing. The boy was the doctor’s son, but the doctor was not the boy’s father. Who was the doctor?

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

Solve the mathematical equation in the picture below.