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PRESENTATION 2 Percents

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PERCENTS Indicates number of hundredths in a whole A decimal fraction can be expressed as a percent by moving the decimal point two places to the right and inserting the percent symbol

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ESTIMATING Example: Express 0.0152 as a percent: Move decimal point two places to right 0.0152 = 1.52 Insert percent symbol 0.0152 = 1.52%

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FRACTIONS TO PERCENTS To express a common fraction as a percent: First, express the fraction as a decimal by dividing the numerator by the denominator Convert the answer to a percent by moving the decimal point two places to the right

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FRACTIONS TO PERCENTS Example: Express as a percent: First convert the fraction to a decimal by dividing Then change the decimal to a percent 0.875 = 87.5%

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PERCENTS TO FRACTIONS To express percent as decimal fraction: Drop the percent symbol Move decimal point two places to the left

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PERCENTS TO FRACTIONS Example: Express as a decimal and round the answer to 4 decimal places Convert the fraction to 0.76 Drop the percent symbol and move the decimal point 2 places to the left: 38.76% = 0.3876

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PERCENTS TO FRACTIONS To express a percent as a common fraction: First convert percent to a decimal fraction Then express the decimal fraction as a common fraction

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PERCENTS TO FRACTIONS Example: Express 37.5% as a common fraction Express 37.5% as a decimal Express 0.375 as a common fraction

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PERCENT TERMS DEFINED All simple percent problems have three parts: Rate is the percent (%) Base represents whole or quantity equal to 100% Word “of” generally relates to the base Percentage is part or quantity of percent of the base Word “is” generally relates to the percentage

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PERCENT TERMS DEFINED Example: Identify base, rate, and percentage What percent of 48 is 12? Problem is asking for rate (percent) The number 48 represents whole and is identified by word “of,” so it is the base The number 12 represents part and is identified by word “is,” so it is the percentage

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FINDING THE PERCENTAGE Proportion formula for all three types of percentage problems: Where: B is the base P is the percentage or part of the base R is the rate or percent

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FINDING THE PERCENTAGE Example: What is 15% of 60? The base, B, is 60: the number of which the rate is taken—the whole or a quantity equal to 100% The problem is asking for the percentage (part): the quantity of the percent of the base

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FINDING THE PERCENTAGE The proportion is: Use cross-products and division:

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FINDING THE RATE Example: What percent of 12.87 is 9.62 rounded to 1 decimal place? The base, B, or whole quantity equal to 100% is 12.87 The percentage, P, or quantity of the percent of the base is 9.620 The rate, R, is to be found

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FINDING THE RATE The proportion is: Cross multiply: Divide:

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FINDING THE BASE Example: 816 is 68% of what number? The rate, R, is 68% The percentage, P, is 816 The base, B, is to be found The proportion is: Solve for B:

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PRACTICAL PROBLEMS A 22-liter capacity radiator requires 6.5 liters of antifreeze to give protection to - 17ºC. What percent of the coolant is antifreeze? Round the answer to the nearest whole percent.

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PRACTICAL PROBLEMS In this problem: The percentage (P) or the part is 6.5 liters The base (B) is 22 liters The rate (R) or percent is unknown Set up the formula and solve

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PRACTICAL PROBLEMS Solve: The antifreeze is 30% of the coolant

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