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Unformatted text preview: f units below 26 must balance the number of units above 26. 50 is 24 units above 26. 12 is 14 units below 26. 28 is 2 units above 26. Therefore, we presently have 26 units (24 + 2) above 26 and only 14 units below 26. Therefore the missing number must be 12 units below 26, making it 14. When the numbers are easy to work with, this method is usually the fastest. Just watch your arithmetic. Exercise 2
Work out each problem. Circle the letter that appears before your answer. 1. Dick’s average for his freshman year was 88, his sophomore year was 94, and his junior year was 91. What average must he have in his senior year to leave high school with an average of 92? (A) 92 (B) 93 (C) 94 (D) 95 (E) 96 The average of X, Y, and another number is M. Find the missing number. (A) 3M – X + Y (B) 3M – X – Y (C) (D) (E)
M + X +Y 3 3. The average of two numbers is 2x. If one of the numbers is x + 3, find the other number. (A) x – 3 (B) 2x – 3 (C) 3x – 3 (D) –3 (E) 3x + 3 On consecutive days, the high temperature in Great Neck was 86°, 82°, 90°, 92°, 80°, and 81°. What was the high temperature on the seventh day if the average high for the week was 84°? (A) 79° (B) 85° (C) 81° (D) 77° (E) 76° If the average of five consecutive integers is 17, find the largest of these integers. (A) 17 (B) 18 (C) 19 (D) 20 (E) 21 4. 2. M–X–Y M–X+Y 5. www.petersons.com 108 Chapter 7 3. WEIGHTED AVERAGE
When some numbers among terms to be averaged occur more than once, they must be given the appropriate weight. For example, if a student received four grades of 80 and one of 90, his average would not be the average of 80 and 90, but rather the average of 80, 80, 80, 80, and 90. Example: Mr. Martin drove for 6 hours at an average rate of 50 miles per hour and for 2 hours at an average rate of 60 miles per hour. Find his average rate for the entire trip. Solution:
6 ( 50 ) + 2 ( 60 ) 8 = 300 + 120 420 1 = = 52 8 8 2 Since he drove many more hours at 50 miles per hour than at 60 miles per hour, his average rate should be closer to 50 than to 60, which it is. In gener...
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 Spring '10
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