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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
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- 25 years
- 11 years
- 13 years
- 15 years
- 25 years
Correct Option: D
The average age of 30 boys = 17 years
Age of replaced boy = 18 years
and another joining, the average age = 16.9 years
total decrease = 17 - 16.9 = 0.1 years
Age of new boy = 18 years – total decrease
Age of new boy = (18 – 0.1 × 30) years = 15 years
Second method to solve this question with the help of given formula :
Here, X = 17 – 16.9 = 0.1 , n = 30
Age of new boy = Age of replaced boy – Xn
Age of new boy = 18 – 0.1 × 30 = 18 – 3
∴ Age of new boy = 15 years
