Replace the question mark with the correct number below.

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?

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

Can you find out which number multiplied by itself will give the output as 12345678987654321?

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

Find the 8 in the below-given Image.

A man is looking at a photograph of someone. His friend asks who it is. The man replies, “Brothers and sisters, I have none. But that man’s father is my father’s son.” Who was in the photograph?

I can write cow in 13 letters.

Can You?

Which fur should we be getting from the Lion?

A detective visits his friend John just to discover that John's neighbour Dr Jacob was murdered. Dr Jacob, who is a mathematician wrote the murderer's name in a code word "Hcqtfz". There were five suspects
1. Ajit
2. Pankaj
3. Ganpat
4. Deenu
5. Hariya

The Detective was instantly able to find the murderer.
Can you?