What four weights can be used to balance from 1 to 30 pounds?

Can you tell a 3D object that has just two surfaces?

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?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

What is at the end of a rainbow?

Replace the letters of words with a number so that the below equation holds true

BASE +
BALL
---------
GAMES
----------

A man dies of old age on his 25 birthday. How is this possible?

Complete the following series. It.s very logical:

1, 4, 5, 6, 7, 9, 11, __?

Why is the Hole below a Lock?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?