What is wrong in the below Picture?

In the picture given below, can you find out which digit will take place of the question mark?

Find out the number of circles in the given picture having Illusion

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?

In Greek mythology, the Sphinx sat outside of Thebes and asked this riddle of all travellers who passed by. If the traveller failed to solve the riddle, then the Sphinx killed him/her. And if the traveller answered the riddle correctly, then the Sphinx would destroy herself. The riddle:

What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?

Oedipus solved the riddle, and the Sphinx destroyed herself.

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

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

Baseball bat and ball cost $100. If the bat cost $99 more than the ball, what is the cost of each?

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

Why Wine Glass Stem is so long?