§ 5.5
Solving Commission, Percent
of Increase or Decrease, and
Interest Problems
Solving Commission Problems
The amount of money a person makes that is a percentage of
the value of sales is called a commission. It is calculated by
multiplying the percentage (called the commission rate) by
the value of the sales.
Commission = commission rate value of sales
Example:
A salesperson has a commission rate of 18.5%. He sells
$43,250 worth of goods. What is his commission?
Commission = commission rate value of sales
= 18.5% $43,250
= 0.18.5 43,250
= 8001.25 His commission is $8,001.25.
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Slide #2
Solving Increase & Decrease Problems
We sometimes need to find the percent by which a number
increases or decreases.
amount of increase
Percent of increase =
original amount
Example:
The cost of a certain car increased from $16,000 last year to
$17,280 this year. What was the percent of increase?
Amount of increase = original amount – new amount
= 17,280 – 16,000 = 1280
amount of increase
Percent of increase =
original amount
1280 The car’s cost
= = 0.08 increased by 8%.
16000
Tobey & Slater, Basic College Mathematics, 5e - Angel, Elementary Algebra for College Students, 6e, # 3
Slide #3
Solving Increase & Decrease Problems
amount of decrease
Percent of decrease =
original amount
Example:
Patrick weighed 285 pounds two years ago. After dieting, he
reduced his weight to 171 pounds. What was the percent of
decrease in his weight?
Amount of decrease = original amount – new amount
= 285 – 171 = 114
amount of decrease
Percent of decrease =
original amount
114 Patrick’s weight
= = 0.4 decreased by 40%.
285
Tobey & Slater, Basic College Mathematics, 5e - Angel, Elementary Algebra for College Students, 6e, # 4
Slide #4
Solving Simple Interest Problems
Interest is money paid for the use of money. The principal
is the amount deposited or borrowed. The interest rate is
per year, unless otherwise stated. If the interest rate is in
years, the time must also be in years.
Interest = principal rate time
I=PRT
Example:
Find the simple interest on a loan of $3600 borrowed at 6% for 8
years.
I=PRT
= 3600 0.06 8
= 1728 The interest earned is $1,728.
Tobey & Slater, Basic College Mathematics, 5e - Angel, Elementary Algebra for College Students, 6e, # 5
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