### Applications of Percent problems

```Ex. 1) A color laser printer marked originally priced
at \$699 goes on sale for 30% off. If Chris has
already saved up \$325, how much more money does
he need to buy the printer at the sale price?
Find the discount.
%
part

100 whole
30
x

100 \$699
20970 100x
\$209.70  x
Find the sale price.
Find how much more
money Chris needs.
Sale price = original – discount
Sale price = \$699 - \$209.70
Sale price = \$489.30
Money needed = sale price – money saved
Money needed = \$489.30 - \$325
Money needed = \$164.30
Ex. 2) A bicycle helmet is priced at \$18.50. If it is
on sale for 10% off and there is 7% sales tax, how
much will it cost after tax?
First, find the sale price at
10% off of the original price.
10 discount

100 original
10
x

100 \$18.50
185  100x
\$1.85  x
Sale price = original – discount
Sale price = \$18.50 – \$1.85
Sale price = \$16.65
Next, find the sale price plus
7% tax.
7
t ax

100 sale price
7
x

100 \$16.65
116.55  100x
\$1.17  x
Total cost = sale price + tax
Total cost = \$16.65 - \$1.17
Total cost = \$17.82
Ex. 3) All appliances at Bargain Outlet are marked down to 70% of the
original price. Fred has a coupon for an additional 18% off of the sale
price. If the original price of a microwave is \$500, how much would Fred
pay for the oven before tax?
First, find the price at 70%
off the original price.
Next, find the price with the
additional 18% off the sale price.
70 sale price

100 original
18
discount

100 sale price
70
x

100 \$500
18
x

100 \$350
35000 100x
6300  100x
\$350  x
The final price is the sale price
\$62  x
Final price = sale price – discount
Final price = \$350 - \$63
Final price = \$287
Ex. 4) Bob offered the salesperson at Furniture
Express \$600 for a new couch. This offer included
8% sales tax. If the salesperson accepts the offer,
what was the cost of couch to the nearest dollar?
The total cost of the couch plus tax is \$600 .
Let x = the cost of the couch
The tax on the couch is 8% of the cost.
8
( x )  0.08 x
100
Total cost = cost of couch + tax
\$600 = x + 0.08x
\$600 = 1.08x
\$555.56 = x
\$556 ≈ x
To the nearest dollar,
the couch costs \$556.
Ex. 5) Between noon and 8:00 p.m., the temperature
dropped from 70o F to 35o F. What was the percent
decrease in temperature between noon and 8:00 p.m.?
Remember, percent of change (increase or decrease) is a
variation of the percent proportion.
% change amountof change

100
original
x
70  35

100
70
70x  100(35)
70x  3500
x  50%
There was a 50% decrease in
temperature between noon and 8:00 p.m.
Ex. 6) The radius of a circle was estimated at
15.6 cm. The actual radius was 15.3 cm. Find
the percent error in the estimation to the nearest
hundredth of a percent.
Percent error is another variation of the
percent proportion.
% error amount of error

100
actual
x
15.6  15.3

100
15.3
15.3x  100(0.3)
15.3x  30
x  1.96%
The percent error of the
estimation was 1.96%.
Ex. 7) What is the amount of simple interest on a
principal of \$580 invested at a rate of 7.5% for 3 years?
The simple interest formula is
I = prt
where
 I = interest
 P = principal, or the amount of money borrowed or invested
 r = annual interest rate expressed as a decimal
 t = time in years
I  prt
 7.5 
I  (\$580)
(3)
 100
I  (\$580)(0.075)(3)
In 3 years, \$130.50 would be
earned in simple interest.
I  \$130.50
```