ObjectiveObjectiveSWBAT estimate percentsSWBAT estimate percents

““Estimating with Percents”Estimating with Percents”

You can use fractions or decimals to You can use fractions or decimals to estimate with percents. estimate with percents.

Estimating Percents with FractionsEstimating Percents with Fractions

PercentPercent 10%10% 20%20% 25%25% 33 % 33 % 50%50% 66 %66 %

FractionFraction

31

32

32

21

31

41

51

101

You can estimate the percent of a number by substituting a fraction that is close to a given percent.

A basketball costs $14.99 at A basketball costs $14.99 at Modell’s. Sports Authority is Modell’s. Sports Authority is offering the same basketball at offering the same basketball at 20% off the regular price of 20% off the regular price of $19.99. Estimate to determine $19.99. Estimate to determine which store is offering the better which store is offering the better deal? deal?

Find 20% of $19.99

00.4$

2051

Compatible numbersCompatible numbers – – numbers that are close and help you numbers that are close and help you use mental math to find the solutionuse mental math to find the solution

Use a fraction and compatible numbers to estimate the Use a fraction and compatible numbers to estimate the percent of each number.percent of each number.

means multiplicationmeans multiplication

25%25% 11 44

Find 25% of 35.Find 25% of 35.36

41

19

436

136

41

34%34% 11 33

Find 34% of 63.Find 34% of 63.

163

31

121

363

163

31

Finding Percent Finding Percent ofof a Numbera Number

8%8% 111010

Find 8% of 261.Find 8% of 261.260

101

126

10260

1260

101

Estimating Percents with DecimalsEstimating Percents with DecimalsAnother way to estimate percents is to find 1% or Another way to estimate percents is to find 1% or 10% of a number. You can do this by moving the 10% of a number. You can do this by moving the decimal point in the number.decimal point in the number.

1% 1% Find of any Find of any number by moving the number by moving the decimal point 2 places to decimal point 2 places to the left.the left.

10% 10% Find of any Find of any number by moving the number by moving the decimal point 1 place to decimal point 1 place to the left.the left.

Find 1% of 45Find 1% of 45

45 45 = 0.45 = 0.45 .0.0Find 10% of 45Find 10% of 45

45 45 = 4.5 = 4.5 .0.0

Use 1% or 10% to estimate the Use 1% or 10% to estimate the percent of each number.percent of each number.

Find 4% of 1818 is about 20, so find 4% of 20.1% of 20 = 20.4% of 20 = 4 · 0.2 = 0.84% of 18 is about 0.8.

4% equals 4 · 1%.

.

Find 29% of 8029% is about 30, so find 30% of 80.10% of 80 = 80.30% of 80 = 3 · 8.0 = 24.029% of 80 is about 24.

30% equals 3 · 10%..

Real-Life ApplicationReal-Life ApplicationTim 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 $60.15% = 10% + 5%10% of $60 = $65% of $60 = $6 ÷ 2 = $3$6 + $3 = $9

Tim should leave about $9 for a 15% tip.

Think: 15% is 10% + 5%.

5% is of 10% so divide $6 by 2.

12

Add the 10% and 5% estimates.

Real-Life ApplicationReal-Life ApplicationAmanda 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%10% of $10 = $15% of $10 = $1 ÷ 2 = $0.50$1 + $0.50 = $1.50

Amanda should leave about $1.50 for a 15% tip.

Think: 15% is 10% + 5%.

5% is of 10% so divide $1 by 2.

12

Add the 10% and 5% estimates.