Replace the question mark with the number below given a simple math problem.

Rearrange the letters in "new door" to make one word.

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

What is the centre of gravity?

A quarter is one-fourth of a dollar but Mr. John has changed the equation as below :

DOLLAR * 4 = QUARTER

Can you replace each letter with a digit to make the above solution correct?

Can you find out the remainder when 3^300 is divided by 5?

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

I have branches, but no fruit, trunk or leaves. What am I?

What is the fastest way to double your money?

I have a big mouth and I am also quite loud! I am NOT a gossip but I do get involved with everyone's dirty business.