What is the next number in this matchsticks series riddle?

I have holes on the top and bottom. I have holes on my left and on my right. And I have holes in the middle, yet I still hold water. What am I?

What number comes next in the series?

5 15 5 18 5 24 14 20 _

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

There was a minor accident with a doctor's son but the doctor noticed no major injury. After the treatment, the father of that doctors son is sitting with the son of the doctor without the doctor being in the room.

How can this be possible?

I am the fastest animal but cannot climb the tree. What am I?

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

Count the number of squares in the picture below.

How many triangles can you count in the figure given?

Guess the hidden movie name?