I can write cow in 13 letters.

Can You?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

If your uncle’s sister is not your aunt, what relation is she to you?

In a stable, there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable

If 21x = 79x, what is the value of x?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

What is the word or phrase?

On a magical land of Mexico , all the animal in the land are rational.

There are 10 tigers and one goat.
Tiger can eat goat but since it's a magical land , the tiger who eats the goat , turns into goat and then can be eaten by the remaining tiger(s).

If we leave them for some time then how many goat and tiger will be there , when we come back ?

Can you start the fire using two pieces of wood?

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?