When my father was 31 I was 8. Now he is twice as old as me. How old am I?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

The more you take me, the more you leave me behind.
Who Am I?

How is the moon similar to a dollar?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

Can you identify the hidden rebus in the image below?

A man hijacks an aeroplane transporting both passengers(8 of them) and valuable cargo. After taking the cargo, the man demands nine parachutes, puts one of them on, and jumps, leaving the other eight behind. Why did he want eight?