New SAT Math Workbook

Simply round off all answers to the nearest multiples

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Unformatted text preview: c. 32(12 + 8) = 32(12) + 32(8) w. Associative Law of Multiplication d. 378 + 0 = 378 x. Identity for Multiplication e. (7 · 5) · 2 = 7 · (5 · 2) y. Distributive Law of Multiplication over Addition z. Commutative Law of Addition www.petersons.com Operations with Whole Numbers and Decimals 11 9. ESTIMATING ANSWERS On a competitive examination, where time is an important factor, it is essential that you be able to estimate an answer. Simply round off all answers to the nearest multiples of 10 or 100 and estimate with the results. On multiple-choice tests, this should enable you to pick the correct answer without any time-consuming computation. Example: The product of 498 and 103 is approximately (A) 5000 (B) 500,000 (C) 50,000 (D) 500 (E) 5,000,000 Solution: 498 is about 500. 103 is about 100. Therefore the product is about (500) (100) or 50,000 (just move the decimal point two places to the right when multiplying by 100). Therefore, the correct answer is (C). Example: Which of the following is closest to the value of 4831 • (A) (B) (C) (D) (E) Solution: Estimating, we have 3500 2 ( 5000 )( 700 ) 2000 710 2314 ? 83 425 1600 3140 6372 5( 700 ) 2 . Dividing numerator and denominator by 1000, we have or , which is about 1750. Therefore, we choose answer (C). Exercise 9 Choose the answer closest to the exact value of each of the following problems. Use estimation in your solutions. No written computation should be needed. Circle the letter before your answer. 1. 483+1875 119 3. 783+ 491 1532−879 (A) (B) (C) (D) (E) 2. 2 10 20 50 100 (A) (B) (C) (D) (E) .02 .2 2 20 200 6017 i 312 364 +618 (A) (B) (C) (D) (E) 18 180 1800 18,000 180,000 www.petersons.com 12 Chapter 1 RETEST 1. Find the sum of 86, 4861, and 205. (A) 5142 (B) 5132 (C) 5152 (D) 5052 (E) 4152 From 803 subtract 459. (A) 454 (B) 444 (C) 354 (D) 344 (E) 346 Find the product of 65 and 908. (A) 59,020 (B) 9988 (C) 58,920 (D) 58,020 (E) 59,920 Divide 66,456 by 72. (A) 903 (B) 923 (C) 911 (D) 921 (E) 925 Find the sum of .361 + 8.7 + 43.17....
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