Question

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 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.

Answer 1

$40$ student = boys $=\frac{3}{4}\times 40=30$

Girls $=1/4\times 40=10$

< age boys> $=20\times 30=600$

< age girl > $=18\times 10=180$

$\Rightarrow$ girls $=15$ boys$=20$

< boys> $=600/20=30$

< girl > $=180/15=12$