Can you replace the question mark with the correct number?

It is always ahead of me yet I can never see it. What is it?

Two old friends, Jack and Bill, meet after a long time.

Three kids
Jack: Hey, how are you, man?
Bill: Not bad, got married and I have three kids now.
Jack: That's awesome. How old are they?
Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.
Jack: Cool..But I still don't know.
Bill: My eldest kid just started taking piano lessons.
Jack: Oh, now I get it.

How old are Bill's kids?

I am Huge on Sunday and Saturday.
I am small from Tuesday to Thursday.
I do not exist on Monday and Friday.
Who am I?

Solve the equation by replacing the alphabet with numbers.

MOM + MOM + NO = BOOK=

The day after tomorrow will be three days before Tuesday. Can you find out what is today?

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

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?

I can be cracked, made, told, and played. What am I?

If an electric train is travelling south, then which way is the smoke going?