If eleven plus two equals one, what does nine plus five equal?

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

What came first, the chicken or the egg?

A boy purchased a book from a bookkeeper and gave him $100.
The cost of the book is $50 but the bookkeeper has no change, so he gets the change from the next shop and returns the boy his $50.

After some time the next shopkeeper came with the $100 note and told the bookkeeper that the note was a fraud, so he took the money back.

How much loss did the bookkeeper face?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?

There are five men, let's say Tarun Harish Lavesh, Manoj, and Manish. All of them have a dot mark on their forehead. They can't see the dots on their forehead but can see the ones on others. The owner of WHITE Dot is an honest person and will never lie, while the owner of BLACK Dot always tells the lie.

This is the statement from Tarun Harish Lavesh and Manish:
Tarun: 'I see 3 whites and 1 black'
Harish: 'I see 4 black'
Lavesh: 'I see 3 black and 1 white'
Manish: 'I see 4 white'

What colour is the dot on each of Tarun Harish Lavesh, Manoj, and Manish's forehead?

What Time Should the last watch show in the below figure?

Can you move 2 matchsticks to form four equal sized squares.

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?