Which number should replace the question mark?

How many sides does a circle have?

What can you see in the middle of March and April that you can never see in any other month?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

He runs but never walks. Murmurs, but never talks. Has a bed, but never sleeps. And has a mouth, but never eats?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

Mr Red Lives in the red house.
Mr Green Lives in the greenhouse.
Mr Yellow Lives in the yellow house.

Who lives in the Whitehouse?

A professor thinks of two consecutive numbers between 1 and 10.
'A' knows the 1st number and 'B' knows the second number

A: I do not know your number.
B: Nor do I know your number.
A: Now I know.

What are the four solutions for this?

Why are all black people so quick ?

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?