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

Can you name some countries which do not have the alphabet 'A' in them?

Why Aeroplane windows are round?

When we see 2 but call 10?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

This is a picture puzzle. You have to guess the name of the movie that can be related to the picture.

Alpha is Beta's sister.

Gamma is a Beta mother.

Delta is Gamma's father.

Tango is Delta's mother.

Then,

How is Alpha related to Delta?

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

I have thought of a number that is made up by using all the ten digits just once. Here are a few clues for you to guess my number:

First digits is divisible by 1.
First two digits are divisible by 2.
First three digits are divisible by 3.
First four digits are divisible by 4.
First five digits are divisible by 5.
First six digits are divisible by 6.
First seven digits are divisible by 7.
First eight digits are divisible by 8.
First nine digits are divisible by 9.
The number is divisible by 10.

Can you find out the number ?

John was working on a Chemical Mixture whose weight comprise 90% liquid and 10% solid. The total weight of the mixture is 20 pounds. After a while, John noticed that some of the liquid evaporated and now the liquid comprises just 50% of the weight.

What is the weight of the chemical mixture now?