7-8 Solving Percents Problems

I CAN use a proportion to solve problems involving percents. I CAN use an equation to solve problems involving percents.

7-8 Solving Percents Problems

Sloths may seem lazy, but their extremely slow movement helps to make them almost invisible to predators. Sloths sleep an average of 16.5 hours a day. To find out what percent of a 24-hour day 16.5 hours is, you can use a proportion or an equation.

7-8 Solving Percents Problems

Proportion Method Equation Method

n100

= 16.524

PartWhole

PartWhole

What percent of 24 is 16.5?

n · 24 = 100 · 16.5

24n = 1,650

n = 68.75

n · 24 = 16.5

n = 0.6875

n = 68.75%

Sloths spend about 69% of the day sleeping!

7-8 Solving Percents Problems

Solve.

Example 1: Using Proportions to Solve Problems with Percents

A. What percent of 40 is 25?n

100= 25

40

n · 40 = 100 · 25

40n = 2,500

40n40

= 2,500 40

n = 62.5

25 is 62.5% of 40.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 40 to undo the multiplication.

7-8 Solving Percents Problems

Solve.

Example 1: Using Proportions to Solve Problems with Percents

B. 15 is 25% of what number?

25100

= 15n

n · 25 = 100 · 15

25n = 1,500

25n25

= 1,500 25

n = 60

15 is 25% of 60.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 25 to undo the multiplication.

7-8 Solving Percents Problems

Solve.

You Try! Example 1

A. What percent of 50 is 10?n

100= 10

50

n · 50 = 100 · 10

50n = 1,000

50n50

= 1,000 50

n = 20

10 is 20% of 50.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 50 to undo the multiplication.

7-8 Solving Percents Problems

Solve.

You Try! Example 1

B. 8 is 40% of what number?

40100

= 8n

n · 40 = 100 · 8

40n = 800

40n40

= 800 40

n = 20

8 is 40% of 20.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 40 to undo the multiplication.

7-8 Solving Percents Problems

Solve.

Example 2: Using Equations to Solve Problems with Percents

A. 35 is 28% of what number?

35 = 28% · n

35 = 0.28 · n

350.28

= 0.28 · n0.28

125 = n

35 is 28% of 125.

Write an equation.

Write 28% as a decimal.

Divide each side by 0.28 to undo the multiplication.

7-8 Solving Percents Problems

Solve.

Example 2: Using Equations to Solve Problems with Percents

B. What percent of 9 is 18?

18 = n · 9

189

= n · 99

2 = n

200% = n

18 is 200% of 9.

Write an equation.Divide each side by 9 to undo the multiplication.Write the decimal as a percent.

7-8 Solving Percents Problems

Solve.

You Try! Example 2

A. 36 is 24% of what number?

36 = 24% · n

36 = 0.24 · n

150 = n

36 is 24% of 150.

Write an equation.

Write 24% as a decimal.

Divide each side by 0.24 to undo the multiplication.

360.24

= 0.24 · n0.24

7-8 Solving Percents Problems

Solve.

You Try! Example 2

B. What percent of 6 is 36?

36 = n · 6

366

= n · 66

6 = n

600% = n

36 is 600% of 6.

Write an equation.Divide each side by 6 to undo the multiplication.Write the decimal as a percent.

7-8 Solving Percents Problems

A portable DVD player costs $225 before tax at an appliance warehouse. What is the sales tax rate if the tax is $18?

Example 3: Finding Sales Tax

n100

= 18225

n · 225 = 100 · 18

8% of $225 is $18. The sales tax is 8%.

Write a proportion.

Set the cross products equal.

Multiply.

Restate the question: What percent of $225 is $18?

225n = 1800

225n225

= 1800225

Divide each side by 225.

n = 8

7-8 Solving Percents Problems

A new flat screen TV costs $800 before tax at an appliance warehouse. What is the sales tax rate if the tax is $56?

You Try! Example 3

n100

= 56800

n · 800 = 100 · 56

7% of $800 is $56. The sales tax is 7%.

Write a proportion.

Set the cross products equal.

Multiply.

Restate the question: What percent of $800 is $56?

800n = 5600

800n800

= 5600 800

Divide each side by 800.

n = 7

7-8 Solving Percents Problems

Reflection

CAN YOU use a proportion to solve problems involving percents? CAN YOU use an equation to solve problems involving percents?

7-8 Solving Percents Problems

Lesson QuizSolve.

1. 21 is 42% of what number?

2. What percent of 292 is 73?

3. 112% of what number is 84?

4. What percent of 1,340 is 13.4?

5. An ad features a bicycle on sale for $139. If the total cost of the bike is $147.34, what is the sales tax rate?

25%

50

75

1%

6%

7-8 Solving Percents Problems

HOMEWORK

p. 324: 1

-9 odd, 10-22 even