What does this rebus mean?

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I am white when I am dirty, and black when I am clean. What am I?

An office is divided into 8 cubicles. How many of the cubicles are painted if only 1/8 of the cubicles are painted?

In the below-given picture of a pretty girl, there is something wrong. Can you find out what it is?

Replace the question mark with the correct number in the below-given picture?

A bag contains 64 balls of eight different colours. There are eight of each colour (including red). What is the least number you would have to pick, without looking, to be sure of selecting 3 red balls?

Today, I celebrated my 32nd birthday but I was born in 1972.
How is this possible?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?