What is the next number in this series?

4,12,84,3612....

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

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?

An American nightclub called 'The Coconut Grove' had a terrible fire in which over 400 people died. A simple design flaw in the building led to a high death toll. Subsequently, regulations were changed to ensure that all public buildings throughout the country eliminated this one detail, which proved deadly. What was it?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

How many triangles can you count in the figure given?

Below, you can see three complete equations and one incomplete. Based on the three complete ones, can you complete the incomplete one?

5 $ 4 $ 3 $ 9 = 4215
6 $ 9 $ 2 $ 6 = 3816
4 $ 7 $ 3 $ 3 = 1122
7 $ 2 $ 7 $ 4 = ____

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

You can see it everyday, But cannot touch it at will. What is it?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?