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.

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

Can you solve the below algebraic mathematical equation?

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

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

Can anyone tell me a word in the English dictionary which has a silent 'z'?

There is something which is always coming but never arrives?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

They are three errirs in this question. Can you find them?

Identify Me

Hint1: I am a god
Hint 2: I am a planet
Hint 3: measurer of heat