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

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

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?

Sherlock breaks into a crime scene. The victim is the owner who is slumped dead on a chair and have a bullet hole in his head. A gun lies on the floor and a cassette recorder is found on the table. On pressing the play button, Sherlock hears the message 'I have committed sins in my life and now I offer my soul to the great Lord' and followed a gunshot Sherlock smiles and informed the police that's its a murder.

Why did he think so?

John speaks the truth only once a day in a week. Below are a few hints for you:

First: Days are Sunday, Monday and so on.
Second: One day he says, "I lie on Monday and Tuesday".
Third: On the next day, he says, "Today is either Thursday, Saturday or Sunday".
Fourth: On the next day, he says, "I lie on Wednesday and Friday".

Can you identify the day on which he speaks the truth?

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?

Find the smallest sentence with all the English alphabet.

Which city is three-fifths chick two third cat and 50% goat?

What demands an answer, but asks no questions

What has many keys but can’t open a single lock?