Count the squares in the matchstick puzzle below?

If all Goats are Sheep and all Sheep are Deers, are all Deers Goats ?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

Jenifer is learning to drive her car. She went down a one way lane and in the wrong direction. But she do not break any law.

How come ?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

You have two buckets of 11 liters and 6 litres.
How can you measure exactly 8 litres?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

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

What numbers should go on the bottom line?
3 6 9 15
8 2 10 12
11 8 19 27
19 10 29 39
? ? ? ?

What does below chemistry rebus means?