Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

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.

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

There are forty elephants and they have forty-fore heads. How can this be possible?

What does below Rebus say?

XLR8

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

Count the number of balls in picture below:

If two's company, and three's a crowd, then whats four and five ?

There are 2 cops parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing.

Why?