Challenge:
The average of five numbers is 11 and the average of eight numbers is 7.75. What is the average of these 13 numbers?
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The correct answer is 9.
The average of five numbers is 11. Therefore, their sum is:
5 × 11 = 55
The average of eight numbers is 7.75. Therefore, their sum is:
8 × 7.75 = 62
The sum of all 13 numbers is 55 + 62 = 117
Therefore, the average of these 13 numbers is:
117 ÷ 13 = 9
Reza is an experienced Math instructor and a test-prep expert who has been tutoring students since 2008. He has helped many students raise their standardized test scores--and attend the colleges of their dreams. He works with students individually and in group settings, he tutors both live and online Math courses and the Math portion of standardized tests. He provides an individualized custom learning plan and the personalized attention that makes a difference in how students view math.
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