I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

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?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

What does this rebus mean?

O
N
C
E
TIME

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

I’m tall when I’m young, and I’m short when I’m old. What am I?

Andrew’s doctor gives him three pills and tells him to take one every half hour. How much time will have passed by the time Andrew’s taken all three pills?

The peacock is a bird that does not lay eggs. How do they get baby peacocks?

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