7-8 Solving Percents Problems Learn 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 n 100 = Part Whole Part Whole What percent of 24 is 16.5? n · 24 = 100 · n = 1,650 n = n · 24 = 16.5 n = n = 68.75% Sloths spend about 69% of the day sleeping!

7-8 Solving Percents Problems Solve. Additional Example 1A: Using Proportions to Solve Problems with Percents What percent of 40 is 25? n 100 = n · 40 = 100 · 25 40n = 2,500 40n 40 = 2, n = is 62.5% of 40. Write a proportion. Set the cross products equal. Multiply. Divide each side by 40 to isolate the variable.

7-8 Solving Percents Problems Solve. Additional Example 1B: Using Proportions to Solve Problems with Percents 15 is 25% of what number? = 15 n n · 25 = 100 · 15 25n = 1,500 25n 25 = 1, n = is 25% of 60. Write a proportion. Set the cross products equal. Multiply. Divide each side by 25 to isolate the variable.

7-8 Solving Percents Problems Solve. Check It Out: Example 1A What percent of 50 is 10? n 100 = n · 50 = 100 · 10 50n = 1,000 50n 50 = 1, n = is 20% of 50. Write a proportion. Set the cross products equal. Multiply. Divide each side by 50 to isolate the variable.

7-8 Solving Percents Problems Solve. Check It Out: Example 1B 8 is 40% of what number? = 8n8n n · 40 = 100 · 8 40n = n 40 = n = 20 8 is 40% of 20. Write a proportion. Set the cross products equal. Multiply. Divide each side by 40 to isolate the variable.

7-8 Solving Percents Problems Solve. Additional Example 2A: Using Equations to Solve Problems with Percents 35 is 28% of what number? 35 = 28% · n 35 = 0.28 · n = 0.28 · n = n 35 is 28% of 125. Write an equation. Write 28% as a decimal. Divide each side by 0.28 to isolate the variable.

7-8 Solving Percents Problems Solve. Additional Example 2B: Using Equations to Solve Problems with Percents What percent of 9 is 18? 18 = n · = n · = n 200% = n 18 is 200% of 9. Write an equation. Divide each side by 9 to isolate the variable. Write the decimal as a percent.

7-8 Solving Percents Problems Solve. Check It Out: Example 2A 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 isolate the variable = 0.24 · n 0.24

7-8 Solving Percents Problems Solve. Check It Out: Example 2B What percent of 6 is 36? 36 = n · = n · = n 600% = n 36 is 600% of 6. Write an equation. Divide each side by 6 to isolate the variable. 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? Additional Example 3: Finding Sales Tax n 100 = 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 = n 225 = 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? Check It Out: Example 3 n 100 = 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 = n 800 = Divide each side by 800. n = 7