The average age of 30 boys in a class is 15 years One boy aged 20 years left the class but two new b...........

Quantitative Aptitude ( CCS) Average

The average age of 30 boys in a class is 15 years. One boy, aged 20 years, left the class, but two new boys came in his place whose ages differ by 5 years. If the average age of all the boys now in the class becomes 15 years, the age of the younger newcomer is

20 years

15 years

10 years

8 years

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Explanation:

Total age of the 30 boys = 30 × 15 = 450
After the boy aged 20 years left, total age = 450 - 20 = 430
Total number of boys = 29
Let the age of the two boys be xx and x+5x+5 respectively
After these boys came, total age =430+x+x+5=435+2x=430+x+x+5=435+2x
Total number of boys = 31
Now the average is given as 15.
Therefore, total age = 31 × 15 = 465
435+2x=465
2x=30
x=15
Age of the younger newcomer = 15 years

Hence, option 2 is the correct answer.