There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

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?

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

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

I have a clock(12-hour format) and both the needles of the clock overlap at 12:00.
After how much time, they will overlap again?

In the image given, you can find several triangles. Can you count them all?

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.

Which point will the car reach to go out?

Find the missing number in the sequence below:

Replace the question mark with the correct number.