The average age of 30 students of a class is 14 years 4 months. After admission of 5 new students in the class the average becomes 13years 9 months. The youngest one of the five new students is 9 years 11 months old. The average age of the remaining 4 new students is:

(1) 11 years 2 months (2) 13 years 6 months (3) 12 years 4 months (4) 10 years 4 months

Solution:

Total age of initial 30 students

= 14years 4 months * 30

= 430 years

Total ageof 35 students

= 13years 9 months * 35

= (455 + 26)years 3 months

= 481 years 3 months

:. Total age of 4 new students

= 481 years 3 months – 430

years- 9 years 11 months

= 481 years 3 months – 439

years 11months

= 41 years 4 months

:. Required average

= 41 years 4 months/4

= 10 years 4 months

Then the option is (4)