Idiot\'s Guides Basic Math and Pre-Algebra

Chapter 7: Ratios, Proportions, and Percentages 91

One last example before we move on. This one asks you to find the part.

What is 83% of 112?

Look for “of.” 112 is the whole. Look for “is.” “What” is the part, that is, the part is unknown. The
percent sign tells you that 83 is the percentage.

83% of 112 is 92.96. Because that decimal terminates after only two places, you can give the exact
answer and not bother with rounding.

If you feel like those examples all seemed very much the same, you’re right. The process is
exactly the same: cross-multiply and divide. The difference is the piece that’s unknown, and, of
course, the numbers themselves.

Percentages can be greater than 100 percent, and that often happens when you turn a question
around. You can say that 2 is 50 percent of 4, or you can reverse the comparison and say 4 is 200
percent of 2. 100 percent is the whole thing, so 200 percent is the whole thing and the whole
thing again, or twice as much. The good news is you do the three types of problems exactly the
same way even if the percentages are greater than 100 percent.

part

whole

%

100

112

83

100

100 112 83

100 9296

92.96

x

x

x

x









CHECK POINT

11. 45 is 20 percent of what number?


12. 16 is what percentage of 64?


13. What is 15% of 80?
    14. 63 is what percentage of 21?
    15. What is 120 percent of 55?