How many sides does a circle have?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

What does this say?

XLR8

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

The great emperor Akbar once ruled India. He was well known for his intelligence. But along with that, he was known for the Nine Gems in his court. One of the nine gems was Birbal, a quick witted and extremely intelligent man. The stories of his wit were widely popular.

Once a king ruling in a distant land heard of Birbal. To check his wit, he sent an invitation and called him to visit his land. Akbar allowed Birbal to go and he took off on the journey.

Upon reaching that kings kingdom, he was welcomed with flowers. He was then escorted to the palace of the king. Upon entering the palace, Birbal found that there were six people sitting in front of him adorning the same robe. They were also lookalike and it was hard to judge who the real king was.

After a couple of minutes, Birbal approached one of them and bowed in front of him greeting him.

That was the real king. How did Birbal know who was the real king ?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

Count the number of squares in the picture below.

On a bright sunny day, two fathers took their son fishing in the lake. Each man and son were able to catch one fish. When they returned to their camp, there were only three fishes in the basket. What happened?

PS: None of the fish were eaten, lost, or thrown back.

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

which number am I?

I am five letter word that is under you.
If you remove my 1st letter, then I am over you.
If you remove my 1st and 2nd letters then I am all around you.

Who am I?