Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

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?

Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

What has no start, end, or centre?

What do you answer even though it never asks you questions?

How do you go from 98 to 720 using just one letter?

I am a type of word that is spelt incorrectly or used differently, on purpose for humour. What am I?
Hint 1: You can find me in a joke.
Hint 2: I am a play on words.

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

Can you calculate the probability of getting a sum of six when a dice is thrown twice?

You knock a Table over in the library, and suddenly 20 eyes are looking at you.