Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

What is always in front of you but can’t be seen?

There is one thing that goes round the house and also inside the house but never even share a brief touch. What is it?

There is an exact a week gap between Christmas and New Year. Hence, It is obvious that the new year that comes right after Christmas comes on the same day of the week.

A Strange thing happened in the Year 1777. Christmas occurs on Wednesday and New Year on Monday. How is that possible?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

10+10 and 11+11 can give you the same answer.

Explain how?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

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 ?

You walk into a room where there are three primates held in their respective cages:
1) A lion who is eating the flesh of a goat.
2) An orangutan who is playing with blocks.
3) A donkey who is sitting idle.

Who is the most intelligent primate in the room?

What is more useful when it is broken?