Transcript Scale Drawings

LESSON 7-2
Warm Up
Lesson 7-1 Warm-Up
ALGEBRA READINESS
LESSON 7-1
Warm Up
Lesson 7-1 Warm-Up
How many
periods are
in a hockey
game?
ALGEBRA READINESS
“Finding a Percent of a Number”
(7-2)
How do you find the
percent of a number?
To find the percent of a number, multiply the number by the percent in its
fraction form or decimal form or use a proportion
Example:Find 22% of 250..
Since “of” in a word problem means “multiply”, we need to multiply the
two numbers. Before you multiply, though, you need to clear the percent
sign by turning the percent into a fraction or a decimal.
Method 1: Multiply by the fraction form of the percent
22
22% =
Write the percent as a fraction.
100 5
22
22
250
250 •
=
•
Divide 250 and 100 by their GCD,
100
100
1
50
2
110
Divide 250 and 100 by their GCD,
2 = 55
Method 2: Multiply by the decimal form of the percent
22% = 0.22
Write the percent as a decimal.
0.22 • 250 = 55
Multiply.
So 22% of 250 is 55
ALGEBRA READINESS
Finding a Percent of a Number
LESSON 7-2
Additional Examples
Find 88% of 250.
Method 1
Write the percent as a decimal.
88% = 0.88
Write 88% as a decimal.
0.88  250 = 220
Multiply.
Method 2
88% =
Write the percent as a fraction.
88
22
=
100
25
10
22
250
22
• 250 =
•
25
251 1
= 220
Write the percent as a fraction in
simplest form.
Divide 25 and 250 by their GCD, 25.
Multiply.
So, 88% of 250 is 220.
ALGEBRA READINESS
Finding a Percent of a Number
LESSON 7-2
Additional Examples
Estimate a 15% tip on a restaurant bill of $17.73.
What you think
1
The bill is about $18. I know 10% of 18 is 10 of 18, or 1.8. Then
5% of 18 is half of 1.8, or 0.9. A 15% tip is about $1.80 plus $.90,
or $2.70.
Why it works
15% of 18 = 0.15 • 18
Rewrite 15% as 0.15
= (0.10 + 0.05) • 18
Rewrite 0.15 as 0.10 + 0.05
= 0.10(18) + 0.05(18)
Use the Distributive Property.
= 1.8 + 0.9
Multiply.
= 2.70
Add.
A 15% tip for a $17.73 bill is about $2.70.
ALGEBRA READINESS
Finding a Percent of a Number
LESSON 7-2
Lesson Quiz
1. Find 81% of 110.
0.81 • 110 = 89.1
2. Use fractions to estimate 74% of 38.
3
• 40 = 30
4
3. Estimate a 15% tip on $8.15.
0.1(8) + 0.1(4) = 0.8 + 0.4 = $1.20
ALGEBRA READINESS