Calculating Percentage Changes
Estimate and find percentages of whole number and decimal amounts.
Number Framework Stage 8
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.