Why do we preferably have round manhole covers and not square ones?

In the picture that is attached with this question, you can find a square which comprises of four little squares inside it. Consider this square to be made with matchsticks. You have to remove two matchsticks such that only two squares remain instead of five.How will you do it ?

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What four weights can be used to balance from 1 to 30 pounds?

A sundial has the fewest moving parts of any timepiece. Which has the most?

Where do fish keep their money?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?