What do you answer even though it never asks you questions?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

Find the next number in the following series:
6, 14, 26, 98, __?

No matter how little or how much you use me, you change me every month. What am I?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?

What happened when the wheel was invented?

You have to fill the below given grid in a manner that every row and column contains the digits 1 to 6. Also, make sure that the squares that are connected with each other must contains the same digit.

A doctor and a boy were fishing. The boy was the doctor’s son, but the doctor was not the boy’s father. Who was the doctor?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Can you convert the number zero(0) into a positive number using just one mathematical operator ?