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

I am sure no one can have two things for dinner. what are they?

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?

What can you hold in your right hand, but never in your left hand?

John was driving a bus and got stuck when passing through an underpass. Then came Jacob with a needle and got the bus out of the underpass.

What did the boy do?

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

You are on a Boat in the mid of a river. You have two cigarettes with you. One of these two you have to light, how will you light the cigarette?

Identify the 10 differences between the two given pictures.

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

A word I know has six letters it contains, remove one letter and 12 remain. What is it?