What does below rebus means ?

Forwards I am heavy, backward I am not. What am I?

If two's company, and three's a crowd, then whats four and five ?

What is the below Rebus indicate?

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?

what's the probability of getting a king or a queen from a pack of 52 cards?

A man stands on one side of a river, his dog on the other. The man calls his dog, who immediately crosses the river without getting wet and without using a bridge or a boat. How did the dog do it?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

Which country gets ill every time?

I know there are two methods by using three time the same number with a plus(+) operator , you can make sum as 60.

One of them is 20+20+20.

whats the other way ?