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The average age of 160 boys in a class is 58 yrs. The average group of 30 boys in the class is 42 yrs and the average of another group of 50 boys in the class is 36 years. What is the average age of the remaining boys? A) 72.58 B) 74.25 C) 77.75 D) 75.68

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The average age of 160 boys in a class is 58 yrs. The average group of 30 boys in the class is 42 yrs and the average of another group of 50 boys in the class is 36 years. What is the average age of the remaining boys? A) 72.58 B) 74.25 C) 77.75 D) 75.68 
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C)

Total age of 160 boys = 160* 58= 9280

total age of 30 boys = 30 * 42= 1260

total age of next 50boys = 50 * 36= 1800

average of the remaining boys =

[(9280-{1260+1800})/[160 - (30 + 50)]

=>9280-3060/80

=>6220/80

=77.75yrs
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