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20% of 50 is what number?
THE 3 TYPES OF BASIC PERCENT PROBLEMS
.20 ( )50 = x10 = x
Number is 10
x = number
30% of 90 is what number?x = number.30 ( )90 = x
27 = x
Number is 27
%%%
20% of what number is 10?
THE 3 TYPES OF BASIC PERCENT PROBLEMS
.20 ( ) x = 10
Number is 50
.20 .20
x = number
x = 50
%%%
6% of what number is 120?x = number.06 ( ) x = 120
Number is 2000
.06 .06x = 2000
10 is what percent of 50?
THE 3 TYPES OF BASIC PERCENT PROBLEMS
10 ( ) x= 50
x = .250 50
20%
x = number
30 is what percent of 80?
30 ( ) x= 80
x = .37580 80
37.5%
x = number
%%%
When an increase or decrease is expressed as a percent, it is called the PERCENT OF CHANGE.
If the new number is greater than the original number, it is called the PERCENT OF INCREASE.
If the new number is less than the original number, it is called the PERCENT OF DECREASE.
PERCENT OF CHANGE
Bill buys a coat on sale for $40. The price before the sale was $50.What was the percent of decrease?
PERCENT OF DECREASE =amountoriginal
changeofamount
PERCENT OF DECREASE = 50
10%20
PERCENT OF CHANGE
AMOUNT OF CHANGE = 50 – 40 = 10
TRY THIS ONE:Mary earned $520 last week. This week she earned $380. What was her percent of decrease?Round to the nearest tenth of a percent.
PERCENT OF DECREASE =amountoriginal
changeofamount
PERCENT OF DECREASE = 520
140%9.26
PERCENT OF CHANGE
AMOUNT OF CHANGE = 520 – 380 = 140
Roberto is buying a car for $23,000. After taxes, he actually pays $24,265. What was the percent of increase (tax rate)?
PERCENT OF INCREASE =amountoriginal
changeofamount
PERCENT OF INCREASE = 23000
1265%5.5
AMOUNT OF CHANGE = 24,265 – 23,000 = 1265
PERCENT OF CHANGE
ADDING SALES TAX
6% of $7.98 =
Jerome buys a dinner for $7.98. What will he pay after adding a sales tax of 6%?
.06($7.98) = $0.4788To what decimal place do we round the answer?
$0.48Now what?
$7.98 + $0.48 = $8.46
PERCENT OF CHANGE
Try multiplying $7.98 by 106%. What do you get?
ADDING SALES TAX - TRY THIS ONE
5.5% of $125 =
Della bought a new coat for $125. What will she pay if a 5.5% sales tax is added?
.055($125) = $6.875To what decimal place do we round the answer?
$6.88Now what?
$125 + $6.88 = $131.88
PERCENT OF CHANGE
Try multiplying $125 by 105.5%. What do you get?
AMOUNT PAID AFTER DISCOUNT
PERCENT OF CHANGE
25% of $78 =
Judy buys a ring for $78. What will she pay after a discount of 25%?
.25($78) = $19.50
Now what?
$78 - $19.50 = $58.50
Try multiplying $78 by 75%. What do you get?
AMOUNT PAID AFTER DISCOUNT – TRY THIS ONE
PERCENT OF CHANGE
15% of $34500 =
Wilford buys a new pickup that usually costs $34,500. He is getting a 15% discount. What will he pay for the pickup (disregard taxes).
.15($34500) = $5175
Now what?
$34500 - $5175 = $29325
Try multiplying $34500 by 85%. What do you get?
SOLVING FOR THE ORIGINAL AMOUNT
PERCENT OF CHANGE
x = original area
Martha increased the flower area in her garden by 22%. She now has 585.6 sq. ft. of flower area. What was the area before the increase?
x + .22x = 585.61.22x = 585.6
x = 480
480 sq. ft.1.22 1.22
SOLVING FOR THE ORIGINAL AMOUNT
PERCENT OF CHANGE
x = original number of stamps
Charles decreased his stamp collection by 15%.He now has a collection of 12,920 stamps.How many stamps did he have originally?
x – .15x = 12920
.85x = 12920
x = 1520015,200 stamps.85 .85
SOLVING FOR THE ORIGINAL AMOUNT
PERCENT OF CHANGE
x = original price
TRY THIS ONE:Theresa bought a dress on sale for $53.04. She knows that it was on sale for 20% off. What was the original price for the dress.
x – .20x = 53.04
.80x = 53.04
x = 66.30
$66.30.80 .80
DOUBLE CHANGES
PERCENT OF CHANGE
FIND THE SALE PRICE
An MP3 player, originally priced at $82.98 is now on sale for 20% off. The sales tax is 6.5%. What will you have to pay for the MP3 player?
.20(82.98) = 16.60
82.98 – 16.60 = 66.38
.065(66.38) = 4.31
$70.69
THEN FIGURE THE TAX.
66.38 + 4.31 = 70.69
