Basic Mathematics for College Students

582 Chapter 6 Percent

55. THE UNITED NATIONS In 2008, the U.N.
    Security Council voted to increase the size of a
    peacekeeping force from 17,000 to 20,000 troops.
    Find the percent of increase in the number of
    troops. Round to the nearest one percent.
    (Source:Reuters)


56. GAS MILEAGE A woman found that the gas
    mileage fell from 18.8 to 17.0 miles per gallon
    when she experimented with a new brand of
    gasoline in her truck. Find the percent of decrease
    in her mileage. Round to the nearest tenth of one
    percent.


57. Fill in the blanks.
    a. Sales tax sales tax rate 
    b. Total cost purchase price 
    c. Commission sales


58. Fill in the blanks.
    a. Amount of discount original price 

b. Amount of discount 

discount rate 

c. Sale price original price 

59. TOOL CHESTS Use the information in the
    advertisement below to find the discount, the
    original price, and the discount rate on the tool
    chest.


60. RENTS Find the discount rate if the monthly rent
    for an apartment is reduced from $980 to $931 per
    month.

Tool Chest

Professional

quality

7 drawers

Save

$180!

Sale price

$2,320

SECTION 6.4 Estimation with Percent

Estimationcan be used to find approximations

when exact answers aren’t necessary.

To find 1% of a number,move the decimal point

in the number two places to the left.

DEFINITIONS AND CONCEPTS EXAMPLES

What is 1% of 291.4? Find the exact answer and an estimate using

front-end rounding.

Exact answer:

1% of Move the decimal point two places to the left.

Estimate:291.4 front-end rounds to 300. If we move the understood

decimal point in 300 two places to the left, we get 3. Thus

1% of 291.4 3 Because 1% of 300 3.

291 .42.914

To find 10% of a number,move the decimal

point in the number one place to the left.

What is 10% of 40,735 pounds? Find the exact answer and an estimate

using front-end rounding.

Exact answer:

10% of Move the decimal point one place to the left.

Estimate:40,735 front-end rounds to 40,000. If we move the understood

decimal point in 40,000 one place to the left, we get 4,000. Thus

1% of 40,7354,000 Because 10% of 40,000 4,000.

40,7354,073.5

To find 20% of a number,find 10% of the

number by moving the decimal point one place

to the left, and then double (multiply by 2) the

result. A similar approach can be used to find

30% of a number, 40% of a number, and so on.

Estimate the answer: What is 20% of 809?

Since 10% of 809 is 80.9 (or about 81 ), it follows that 20% of 809 is

about , which is 162. Thus,

20% of 809  162 Because 10% of 809 81.

2  81