The average age of 80 boys in a class is 19 years. The average age of a group of 15 boys in the class is 21 years and the average age of another group of 25 boys in the class is 18 years. What is the average age of the remaining boys in the class?
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18.5 years
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17.5 years
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18.875 years
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19.25 years
C
Correct answer
Explanation
Total age of 80 boys = 80 × 19 = 1520 years. Age of first group (15 boys) = 15 × 21 = 315 years. Age of second group (25 boys) = 25 × 18 = 450 years. Remaining boys = 80 - 15 - 25 = 40 boys. Their total age = 1520 - 315 - 450 = 755 years. Average age of remaining boys = 755 ÷ 40 = 18.875 years. Option C is correct.