New SAT Math Workbook

3 4 what is of 40 5 a 8 b 8 c 08 d 008 e

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Unformatted text preview: ) (B) (C) (D) (E) 100 s r rs 100 100r s r 100 s s 100r 1 2. 5. 3. (A) (B) (C) (D) (E) 20 2 200 16 32 www.petersons.com 76 Chapter 5 3. FINDING A NUMBER WHEN A PERCENT OF IT IS GIVEN This type of problem may be solved using the proportion method, although this may again result in the unnecessary use of time. It is often easier to translate the words of such a problem into an algebraic statement, using decimal or fractional equivalents for the percents involved. Then it will become evident that we divide the given number by the given percent to solve. Example: 7 is 5% of what number? Proportion Method 5 7 = 100 x 5 x = 700 x = 140 Equation Method 7 = .05 x 700 = 5 x 140 = x Example: 40 is 66 % of what number? Proportion Method 2 3 = 40 100 x 2 66 x = 4000 3 200 x = 4000 3 200 x = 12000 2 x = 120 66 x = 60 2 3 Equation Method 2 x 3 120 = 2 x 60 = x 40 = Just think of the amount of time you will save and the extra problems you will get to do if you know that 66 % is 2 and use the equation method. Are you convinced that the common fraction equivalents in the previously 3 2 3 given chart should be memorized? www.petersons.com Percent 77 Exercise 3 Work out each problem. Circle the letter that appears before your answer. 1. 72 is 12% of what number? (A) 6 (B) 60 (C) 600 (D) 86.4 (E) 8.64 80 is 12 % of what number? (A) (B) (C) (D) (E) 3. 37 10 100 64 640 6400 (D) (E) 5. 1 2 4. m is p% of what number? (A) (B) (C) mp 100 100 p m m 100 p p 100 m 100 m p 2. 50% of what number is r? (A) (B) (C) (D) (E) 1 r 2 1 % of what number is 27? 2 (A) (B) (C) (D) (E) 72 1 10 8 5r 10r 2r 100r 90 101.25 216 www.petersons.com 78 Chapter 5 4. TO FIND WHAT PERCENT ONE NUMBER IS OF ANOTHER This type of problem may also be solved using the proportion method. However, this may again result in the use of an unnecessary amount of time. It is often easier to put the part over the whole, simplify the resulting fraction, and multiply by 100. Example: 30 is what percent of 1500? Proportion Method x 30 = 100 1500 1500 x = 3000 x = 2% Fraction Method 30 3 1 =...
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