Can you fill the blank with the correct number?

6 30 870 756030 _____

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

What are the next two letters in the following series and why?
W A T N T L I T F S _ _

*Hint: Check Puzzle Title

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

Count the number of triangles in the given picture.

An old Woman left INR 33,333 to be divided equally among two fathers and two sons and each was to receive INR 11,111.
How was this possible?

On a certain day, John celebrated his birthday. Two days later, his older twin brother Jacob celebrated his birthday.

Is this even possible? How can it be?

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?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.