What percentage of people speaks english

Around 25% percent of people have an understanding of English.

In America, 80% of the population speaks English.
In the World, 25% of the population have some understanding of English.

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .