People make me, save me, change me, raise me. What am I?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

Three ants are going up a hill, one behind the other. The last ant then says to the other ants, 'There is an ant behind me!'' How come?

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

There were two grandmothers and their two granddaughters.
There were two husbands and their two wives.
There were two fathers and their two daughters.
There were two mothers and their two sons.
There were two maidens and their two mothers.
There were two sisters and their two brothers.
Yet there are only six, who are buried here,
All are born legitimate and relationships clear.
How can this happen?

There is one four-digit whole number n, such that the last four digits of n2 are the original number n

Luis Garavito killed Density x Volume.

Who is Luis Garavito ?

A detective visits his friend John just to discover that John's neighbour Dr Jacob was murdered. Dr Jacob, who is a mathematician wrote the murderer's name in a code word "Hcqtfz". There were five suspects
1. Ajit
2. Pankaj
3. Ganpat
4. Deenu
5. Hariya

The Detective was instantly able to find the murderer.
Can you?

Today, I celebrated my 32nd birthday but I was born in 1972.
How is this possible?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?