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.

The below given figure comprises of a pattern through which you can determine the missing letter. Can you push your mind to find the pattern and add the missing letter?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?

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

which number am I?

What is the next number in this series?

4,12,84,3612....

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

What can go up a chimney down, but can’t go down a chimney up?

The host of a game show, offers the guest a choice of three doors. Behind one is a expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?