The easiest way to calculate percentage is to divide the whole into the part and multiply the answer by 100. If a student gets 20 out of 25 questions correct, his percent correct is calculated by dividing 20 by 25 for a total of 0.8 and multiplying by 100.
The student got 80 percent of the questions correct. Percent means "per 100." If a student makes 80 percent on a test, this means that he would get 80 out of every 100 (or four out of every five if expressed in lowest terms) answers correct.
If a student wants to know how many correct answers out of 25 questions he needs to get to make 72 percent, the equation reads "x divided by 25 equals 0.72," since 72 percent is the equivalent of 0.72. Multiplying both sides by 25 yields x, equal to 18. Therefore the student needs 18 correct answers.