pre-algebra. lesson 6-7 warm-up pre-algebra what is “percent of change”? how do you find the...
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PRE-ALGEBRA
PRE-ALGEBRA
Lesson 6-7 Warm-Up
PRE-ALGEBRA
What is “percent of change”?
How do you find the percent of increase or decrease?
percent of change: percent of quantity increase or decrease from the original amount.
To find the percent of increase or decrease, use a proportion or find the difference between the change and the original amount and divide by the original amount
Rule:
Example: Find the percent of decrease from 70 to 63.
Method 1: Proportion
# %
Part (Known) 7 x
Whole (Unknown) 70 100
= Proportion .7
70x
100 70 • x = 7 • 100 Cross products are equal.
70 - 63 = 7 Find the amount of decrease
= Divide both sides by 70. .70070
x = 10 70 to 63 is a 10% decrease
1
1 10
1
Percent of Change (6-7)
PRE-ALGEBRA
How do you find the percent of a number?
Method 2: Divide the difference by 100
Find the difference (subtract) between the original amount the new amount. Then, divide by the original amount
70 - 6370
0 1 _ . Multiply by 100 or move the decimal 2 places to the right to change a decimal into a percent.
= Fraction bars also indicate division, so divide 7 by 70
.
770 0.1
70 to 63 is a 10% decrease
1 0 . % Fill in skipped blank spaces with zeros.
Percent of Change (6-7)
PRE-ALGEBRA
Find the percent of increase from 8 to 9.6.
amount of increase = 9.6 – 8 = 1.6
= 0.2 = 0 . 2 0 . = 20%
The percent of increase from 8 to 9.6 is 20%.
percent of increase = amount of increase
original amount
=1.68
Percent of ChangeLESSON 6-7
Additional Examples
PRE-ALGEBRA
In a given year, Hillsboro had a total of 7.5 in. of rain
by March 1 and a total of 22.5 in. by July 1. Find the percent of
increase from 7.5 to 22.5.
amount of increase = 22.5 – 7.5 = 15
= 2. = 2 0 0.% = 200%
The percent of increase from March 1 to July 1 was 200%.
percent of increase = amount of increase
original amount
=157.5
Percent of ChangeLESSON 6-7
Additional Examples
PRE-ALGEBRA
Find the percent of decrease from 1,250 to 1,120.
amount of decrease = 1,250 – 1,120 = 130
= 0.104 = 0 1 0 4 = 10.4%
percent of decrease = amount of decrease
original amount
= 1301,250
Percent of ChangeLESSON 6-7
Additional Examples
PRE-ALGEBRA
Solve.
1. Find the percent of increase from 22 to 63.
2. Find the percent of decrease from 6.3 to 2.2.
3. A surgeon performed 62 operations in 1991. He performed 342 in 2001. Find the percent of increase.
186.4%
451.6%
65.1%
Lesson Quiz
Percent of ChangeLESSON 6-7