1. Warm Up 1. What percent of 20 is 18? 2. What percent of 400 is 50? 90%
12.5% 33 1 3 %
625%

2. Problem of the Day
The original price of a sweater is $40. The sweater goes on sale for 75% of its original price. Later, the sweater goes on clearance for 50% of its sale price. What is the clearance price of the sweater?
$15

3. TB P
Learn to find a number when the percent is known.

4. Carcharocles megalodon, a giant shark that became extinct almost 3 million years ago, had teeth as large as 7.25 inches along an edge. This is 240% bigger than the largest teeth of a modern great white shark.
When one number is known, and its relationship to another number is given by a percent, the other number can be found.

5. Additional Example 1: Finding a Number When the Percent Is Known
60 is 12% of what number?
Choose a method: Set up an equation to find the number.
60 = 12%  n
Set up an equation. 12
100
12% =
60 = 0.12n
= n 60
0.12
Divide both sides by 0.12.
500 = n
Simplify.
60 is 12% of 500.

6. Additional Example 2: Application
Anna earned 85% on a test by answering 17 questions correctly. If each question was worth the same amount, how many questions were on the test?
Choose a method: Set up a proportion to find the number.
Think: 85 is to 100 as 17 is to what number? = 85
100 17 n
Set up a proportion.

7. Additional Example 2 Continued
85  n = 100  Find the cross products.
85 n = 1700
Simplify.
n = Divide both sides by 85.
1700 85
n = 20
Simplify.
There were 20 questions on the test.

8. Additional Example 3A: Life Science Application
When a giraffe is born, it is approximately 55% as tall as it will be as an adult. If a baby giraffe is 5.2 feet tall when it is born, how tall will it be when it is full grown, to the nearest tenth of a foot?
Choose a method: Set up a proportion.
Think: 55 is to 100 and 5.2 is to what number? = h
5.2 55
100
Set up a proportion.

9. Additional Example 3A Continued
55  h = 100  Find the cross products.
55h = 520
520 55 h =
Divide both sides by 55.
h  9.5
Simplify.
This giraffe will be approximately 9.5 feet tall when full grown.

10. Additional Example 3B: Life Science Application
A fisherman caught a lobster that weighed 11.5 lb. This was 70% of the weight of the largest lobster that fisherman had ever caught. What was the weight, to the nearest tenth of a pound, of the largest lobster the fisherman had ever caught?
Choose a method: Set up an equation.
Think: 11.5 is 70% of what number?
11.5 = 70%  n Set up an equation.

11. Additional Example 3B Continued
Divide both sides by .70.
11.5
0.70 n =
16.4  n
Simplify.
The largest lobster the fisherman had ever caught was about 16.4 lb.

12. Three Types of Percent Problems
You have now seen all three types of percent problems.
Three Types of Percent Problems
1. Finding the percent of a number.
15% of 120 = n =
2. Finding the percent one number is of another.
p% of 120 = =
3. Finding a number when the percent is known.
15% of n = =
n 120
p 100
18 n

13. Lesson Quiz 1 2
1. 10 is 12 % of what number?
is 25% of what number?
3. 44% of what number is 11?
4. 290% of what number is 145?
5. Larry has 9 novels about the American Revolutionary War. This represents 15% of his total book collection. How many books does Larry have in all? 80
1304 25 50 60