20% is 20/100 and of means multiplication so
20% of 55,000 is
20/100*55,000=11000
To find a percentage of things means that if that thing were to be divided into a hundred, how many parts will make up that percentage?
For instance if you have a big loaf of bread and 50% is to be given to your little brother, divide the bread into a hundred parts and give 50 to him.
50% of 100=50