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California Standards

Learn how to calculate percentages using fractions to estimate discounts, tips, and interest. Practice consumer math scenarios for practical applications. Improve your mental math skills with easy-to-follow examples.

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California Standards

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  1. California Standards NS1.4 Calculate given percentages of quantities and solve problems involving discounts at sales, interest earned, and tips. Also covered: NS2.1

  2. The table shows common percents and their fraction equivalents. You can estimate a percent of a number by substituting a fraction that is close to a given percent. Percent 1 3 2 3 10% 20% 25% 33 % 50% 66 % Fraction 1 4 1 5 1 3 2 3 1 10 1 2

  3. Remember! Compatible numbers are close to the numbers in the problem and help you use mental math to find a solution. Additional Example 1: Using Fractions to Estimate Percents Use a fraction to estimate 27% of 63. Think: 27% is about 25% and 25% is equivalent to . 1 4  63 27% of 63  1 4 1 4 Change 63 to a compatible number.  60  Multiply.  15 27% of 63 is about 15.

  4. Check It Out! Example 1 Use a fraction to estimate 48% of 91. Think: 48% is about 50% and 50% is equivalent to . 1 2  91 48% of 91  1 2 1 2 Change 91 to a compatible number.  90  Multiply.  45 48% of 91 is about 45.

  5. Additional Example 2: Consumer Math Application Tara’s T’s is offering 2 T-shirts for $16, while Good-T’s is running their buy one for $9.99, get one for 50% off sale. Which store offers the better deal? First find the discount price for 2 t-shirts at Good T’s. 1 2 1 2  $9.99 50% of $9.99 = Think: 50% is equivalent to . 1 2 Change $9.99 to a compatible number.  $10   $5 Multiply. The second shirt cost approximately $5. Since $10 + $5 = $15, the 2 T-shirts for $15 at Good-T’s is the better deal.

  6. Check It Out! Example 2 Billy’s Office Supply Store is offering 25% off a leather notebook, originally priced at $9.75. K’s Office Supply Store offers the same notebook, not on sale, at $7.00. Which store offers the better deal? First find the discount on the notebook at Billy’s Office Supply. 1 4 1 4  $9.75 25% of $9.75 = Think: 25% is equivalent to . 1 4 Change $9.75 to a compatible number.  $10   $2.50 Multiply. The discount is approximately $2.50. Since $10 – $2.50 = $7.50, the notebook from K’s Office Supply Store is the better deal.

  7. Another way to estimate percents is to find 1% or 10% of a number. You can do this by moving the decimal point in the number. . 0 45 1% of 45 = 10% of 45 = 45 . . . To find 1% of a number, move the decimal point two places to the left. To find 10% of a number, move the decimal point one place to the left.

  8. Additional Example 3: Estimating with Simple Percents Use 1% or 10% to estimate the percent of each number. A. 4% of 18 18 is about 20, so find 4% of 20. 1% of 20 = 20. . 4% of 20 = 4  0.2 = 0.8 4% equals 4 · 1%. 4% of 18 is about 0.8.

  9. Additional Example 3: Estimating with Simple Percents Use 1% or 10% to estimate the percent of each number. B. 29% of 80 29% is about 30, so find 30% of 80. 10% of 80 = 80. . 30% of 80 = 3  8.0 = 24.0 30% equals 3 · 10%. 29% of 80 is about 24.

  10. Check It Out! Example 3 Use 1% or 10% to estimate the percent of each number. A. 5% of 14 14 is about 15, so find 5% of 15. . 1% of 15 = 15. 5% of 15 = 5  0.15 = 0.75 5% equals 5 · 1%. 5% of 14 is about 0.75.

  11. Check It Out! Example 3 Use 1% or 10% to estimate the percent of each number. B. 21% of 60 21% is about 20, so find 20% of 60. . 10% of 60 = 60. 20% of 60 = 2  6.0 = 12.0 20% equals 2 · 10%. 21% of 60 is about 12.

  12. 1 2 5% is of 10% so divide $6 by 2. Additional Example 4: Consumer Math Application Tim spent $58 on dinner for his family. About how much money should he leave for a 15% tip? Since $58 is about $60, find 15% of $60. Think: 15% is 10% + 5%. 15% = 10% + 5% 10% of $60 = $6 5% of $60 = $6 ÷ 2 = $3 $6 + $3 = $9 Add the 10% and 5% estimates. Tim should leave about $9 for a 15% tip.

  13. 1 2 5% is of 10% so divide $1 by 2. Check It Out! Example 4 Amanda spent $12 on a hair cut. About how much money should she leave for a 15% tip? Since $12 is about $10, find 15% of $10. 15% = 10% + 5% Think: 15% is 10% + 5%. 10% of $10 = $1 5% of $10 = $1 ÷ 2 = $0.50 $1 + $0.50 = $1.50 Add the 10% and 5% estimates. Amanda should leave about $1.50 for a 15% tip.

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