Calculating Percentage Changes

The need to calculate percentages is often not obvious to students. It really is a

method of comparing fractions by giving both fractions a common denominator,

namely hundredths. So it is useful way to view percentages as hundredths.

Using Number Properties

Problem: “Tom’s Toothbrush Company makes a profit of $57,892.12 on sales of

$456,789.23. A much bigger company United Industries makes a profit of

$453,884.01 on sales of $4,489,000.89.

Turn the fraction profit of each company into a percentage to see which company

makes a better profit. Round the answers sensibly.”

(Answer: Tom’s fractional profit is 57892.12/456789.23 = 0.126737051 ≈ 0.127 =  12.7%. United Industries’ fractional profit is 453884.01/4489000.89 = 0.101110251  ≈ 0.101 = 10.1%. So Tom’s company makes a slightly better profit.)

Examples: Worksheet (Material Master 8–18).

Understanding Number Properties:

Make up two fractions that are close to each

other and use percentages to show which fraction is larger.