Chapter 8 linear appliCaTionS 227

The data used in the following examples and practice problems can be found
in the 129th edition of Statistical Abstract of the United States. Many quantities
and percentages are approximate.

EXAMPLE

In 2007, the average income for a U.S. adult, age 25 to 34, whose highest

education level was completing high school was $28,982. For a U.S. adult

of the same age having a bachelor’s degree, the average income that

same year was 66.5% more. What was the average income for a U.S. adult,

age 25 to 34 in 2007 whose highest education level was bachelor’s

degree?

We want to compute the following:

HS Grad Income + 66.5% HS Grad Income = Bachelor’s Degree Income

28,982 + (0.665)(28,982) = Bachelor’s Degree Income

28,982 + 19, 273 = 48,255

The average income in 2007 for U.S. adults, age 25 to 34, having a bachelor’s

degree was $48,255.

On January 1, 2010, the price of a first class postage stamp was $0.44,

which is a 37.5% increase from the cost on January 1, 1995. What was the

cost of a first class stamp on January 1, 1995?

EXAMPLE

In 2007, the average income for a U.S. adult, age 25 to 34, whose highest

still struggling

in the first example, the percent was multiplied by the number given; and in the

second example, the percent was multiplied by the unknown. be very careful

when deciding from which quantity you take the percent. Suppose the first

problem were worded, “an item is marked down 20% for a sale. The sale price is

$60, what is the original price?” The equation to solve would be x – 0.20x = 60,

where x represents the original price. a common mistake is to take 20% of $60

and not 20% of the original price.

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