how can I know the easy ways to solve problems on probability

First of all you should know what is probability and how it works.. Let me explain you first what is probability-
Probability is the chance that an event will occur. Events may be any occurence such as:
Going to the doctor,
Standing on a yellow brick or
Seeing a monkey.
As you can guess, the chance of these events happening changes based on other things that are going on at the time. These "other things" are called variables..

Try the probability questions as much you can solve .... try harder and learn short tricks and formulas..