In a class, there are 40 boys and their average age is 16 years. One boy, aged 17 years, leaving the class and another joining, the average age becomes 15.875 years. The age of the new boy is :
Options:
A . 14.5 years
B . 12 years
C . 17 years
D . 15 years
Answer: Option B Answer: (b)Total age of 40 boys = 40 × 16 = 640 years New total age of 40 boys = 40 × 15.875 = 635 years ∴ Age of new boy = [635 – (640–17)] = 12 years Aliter : Using Rule 23, Here, n = 40, x = 16 – 15.875, x = 0.125 Age of new boy = Age of replaced boy–xn = 17 – 0.125 × 40 = 17 – 5 = 12 years
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