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

Forwards I am heavy, backward I am not. What am I?

I cannot talk, but I always reply when spoken to. What am I?

One day Jenifer meets the Lion and the Tiger in the Forest of Forgetfulness. She knows that the Lion lies on Mondays, Tuesdays, and Wednesdays, and tells the truth on the other days of the week. The Tiger, on the other hand, lies on Thursdays, Fridays, and Saturdays, but tells the truth on the other days of the week. Now they make the following statements to Jenifer:

Lion: Yesterday was one of my lying days.

Tiger: Yesterday was one of my lying days too.

What day is it?

How many words can a quill made with the feather of a pigeon write with a 100ml bottle of black ink?

How old is your son? asked a man to his neighbour. My son is five times as old as my daughter and my wife is five times as old as my son. I am twice as old as my wife whereas my grandmother, who is celebrating her eighty-first birthday is as old as all of us put together.

How old is the man's son ?

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

John was driving a bus and got stuck when passing through an underpass. Then came Jacob with a needle and got the bus out of the underpass.

What did the boy do?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.