Why is Saturday stronger than Monday?

Find the missing number in the image below.

I am lying and I always lie. Tell me whether I am lying or telling the truth.

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

I speak without a mouth, and hear without ears. I have no-body, but I come alive with the wind. What am I?

Can you start the fire using two pieces of wood?

I can be cracked, made, told, and played. What am I?

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?

What is the fastest way to double your money?

In the image below, you can see two glasses and two matchsticks.You need to move four matchsticks in such a manner that the crosses come inside the glasses. Note: you cannot move the crossed.