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.

An inspection by the superintendent of St. Joseph School was scheduled on the next day. The class teacher Jenifer knew that he would be asking questions from her class and she would have to choose a pupil to answer. To offer a perfect impression over him, the teacher explained certain instructions to the students to maximise the chances of getting correct answer every time.

What did she say to the students?

I am white when I am dirty, and black when I am clean. What am I?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

Can you solve the below algebraic mathematical equation?

(J+O+I+N+T)3 = JOINT

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?

Why Aeroplane windows are round?

It begins where the time ends.
Its second is an expression of surprise.
Its third is a question.
Its fourth is urinate.
It ends with a drink.

Which country it is?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

Can you name some countries which do not have the alphabet 'A' in them?