Basic Mathematics for College Students

104 Chapter 1 Whole Numbers

EXAMPLE (^4) Long-Distance Calls
The rates that Skype charges for overseas landline
calls from the United States are shown to the right.
A newspaper editor in Washington, D.C., made a
60-minute call to Canada, a 45-minute call to
Panama, and a 30-minute call to Vietnam. What
was the total cost of the calls?
Analyze

• The 60-minute call to Canada costs 2 cents
  per minute. Given


• The 45-minute call to Panama costs 12 cents per minute. Given


• The 30-minute call to Vietnam costs 38 cents per minute. Given


• What is the total cost of the calls? Find
  Form We translate the words of the problem to numbers and symbols. Since the
  word perindicates multiplication, we can find the cost of each call by multiplying
  the length of the call (in minutes) by the rate charged per minute (in cents). Since
  the word totalindicates addition, we will add to find the total cost of the calls.

is equal to plus plus

60(2) 45(12) 30(38)

SolveTo evaluate this expression (which involves multiplication and addition),

we apply the order of operations rule.

The units are cents.

Do the multiplication first.

Do the addition.

StateThe total cost of the overseas calls is or $18.00.

CheckWe can check the result by finding an estimate using front-end rounding.

The total cost of the calls is approximately

500¢1,200¢or 1,820¢.The result of 1,800¢seems reasonable.

60(2¢)50(10¢)30(40¢)120¢ 

1,800¢,

1,800

 120  540 1,140

The total cost

of the calls

60(2)45(12)30(38)

  

The total

cost of

the calls

the cost of

the call to

Vietnam.

the cost of

the call to

Panama

the cost of

the call to

Canada

The total

cost of

the calls

Self Check 4

LONG-DISTANCE CALLS A

newspaper reporter in Chicago

made a 90-minute call to

Afghanistan, a 25-minute call to

Haiti, and a 55-minute call to

Russia. What was the total cost of

the calls?

Now TryProblem 105

All rates are per minute.

Landline calls

Includes tax

Afghanistan

Canada

Haiti

Panama

Russia

Vietnam

41¢

2¢

28¢

12¢

6¢

38¢

2 Evaluate expressions containing grouping symbols.

Grouping symbolsdetermine the order in which an expression is to be evaluated.

Examples of grouping symbols are parentheses brackets braces and

the fraction bar^.

( ), [ ], { },

EXAMPLE (^5) Evaluate each expression: a. b.
StrategyTo evaluate the expression in part a, we will perform the subtraction
first. To evaluate the expression in part b, we will perform the addition first.
WHYThe similar-looking expression in part b is evaluated in a different order
because it contains parentheses. Any operations within parentheses must be
performed first.

12  3  5 12 (35)

Self Check 5

Evaluate each expression:

a.

b.

Now TryProblem 33

20 (76)

20  7  6

1

1

20

540

 1,140

1,800