How can you take 2 from 5 and leave 4?

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?

What does this rebus mean?

O
N
C
E
TIME

When 99 is considered higher than 100?

A maths symbol is hidden in the below Bar Graph. Can you decipher it?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

Astrology starts with the alphabet A, Biology starts with B, Psychology with P and Limnology with L.

Can you find an "ology" that begins with a P?

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

Why Aeroplane windows are round?

I organized a small get together at my home.
In the party , i have a barrel with some whiskey in it.

Suddenly Guest 1 say 'I bet this barrel of whiskey is more than half full'.
'No, it's less than half full' Guest 2 replied.

I don't have any measuring instrument and without removing whiskey from it , how can i determine which of the guest is right ?