What number should come in place of the question mark below?

The centre of the third figure is empty. What digit should fit inside?

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?

How is the moon similar to a dollar?

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.

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

There is a brick of gold and a brick of iron in a boat (both 10-inch blocks), if they are both dropped into the water which will make the water level higher?

Manish has to secure 40% marks to pass his B.tech final exams.
He got just 40 marks and failed by 40-marks.

What is the maximum marks?

What does the below rebus riddle means?

Spelt forwards I’m what you do every day, spelled backwards I’m something you hate. What am I?