In a class there are 30 boys and their average age is 17 years. On one boy aged 18 years leaving the class and another joining, the average age becomes 16.9 years. The age of new boy is
Options:
A . 11 years
B . 25 years
C . 15 years
D . 13 years
Answer: Option C Answer: (c)Age of new boy = 18 years – total decrease = (18 – 0.1 × 30) years = 15 years Aliter : Using Rule 23, ( If in a group, one member is replaced by a new member, then, Age of new member = ( age of replaced member) ± xn where, x = increase (+) or decrease (–) in average n = Number of members. )Here, x = 17 – 16.9 = 0.1, n = 30Age of new boy = Age of replaced boy–xn = 18 – 0.1 × 30 = 18 – 3 = 15 years
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