question_answer

In a school, there are 40 students in which boys and girls are in the ratio 3:1. The mean age of the boys is 20 years and the mean age of the girls is 18 years. If there is increase in girls by 5 and decrease in boys by 10, then find the new average age (approx.) when the students joining or leaving doesn't change the average age of boys and girls respectively.

A)  15 years                      

B)  19 years          

C)         16 years          

D)         Can't say                     

Correct Answer: B

Solution :

Let number of boys and girls be and  respectively. Total number of students = 40 Number of boys And number of girls = 10 Now, after decreasing 10 boys, number of boys is 20. Average age of 20 boys = 20 years. Sum of age of 20 boys Also, after increasing 5 girls, number of girls is 15. Average age of 15 girls = 18 years Sum of age of 15 girls Now, total number of students Average age of students years (approx.)