CHAPTER7 Ratios, Proportions, and Percentages
In This Chapter
- How to compare numbers
by creating ratios - Using ratios to solve
problems - Using proportions to find
unknown numbers - Changing a ratio to a
percentage - How to calculate interest,
tax, and tips
We have two basic ways of comparing numbers: an addition/
subtraction method and a multiplication/division method.
The addition/subtraction method makes statements like 15
is 7 more than 8, or 49 is 1 less than 50. The multiplication/
division method compares numbers by saying things like 63 is
3 times as large as 21, or 12 is half of 24.
In this chapter, you’ll focus on that comparison by multiplica-
tion and division. You’ll learn to use ratios and extended
ratios to help you figure out unknown numbers, and you’ll
solve proportions by cross-multiplying. Once you understand
percentages, you’ll be able to explore how they’re using in
different kinds of problem solvingProportional Reasoning ...........................................................................................................
Twice the size, half as many, three times as much. In your
daily language, you frequently use the idea of multiplying
or dividing as a way to compare numbers. Usually, in con-
versation, you’ll make the comparison using a simple whole
number compared to 1: twice the size or three times as much.
Or you might use division in the form of a simple fraction,
like half as many. But you could make other comparisons, not
always comparing to 1.