What are the three formulas for calculating any percentage question on a calculator?

Question

There are (as I recall), three mathmatical formulas that can be used to calclulate the answer to any percentage question.  What are they?

Answer 1

For converting a fraction into a percentage multiply by 100. Example: 1/4 multiplied by 100 is 25 percent.

For converting a percentage into a fraction, divide by 100. Example: 75% is 75/100=3/4.

Formula 1. For answering the question: What number is p% of n? Call the number y, then y=np/100. Example: what number is 2% of 450? y=450*2/100=9.

Formula 2. For answering the question: y is what percent of n? Call the percentage p. y=np/100, so p=100y/n. Example: 15 is what percent of 250? p=100*15/250=6%.

Formula 3. For answering the question: y is p% of what number? Call the number n=100y/p. Example: 16 is 12.5% of what number? n=100*16/12.5=128.

Note that there's really only one formula, which converts a percentage into a fraction. It's just a matter of taking the two known quantities and rearranging the formula to find the missing unknown.