Average weights of 12 students in a class is 30kgs. two boys are left and two boys are joined with average of 25.if new average is (30+5/6) what is average of two boys left?

sum of total boys =12×30=360 if two boys are replaced with average 25 of two boys, 360+sum of replaced boys-replacing boys=sum of new value 360+50-replacing boys sum=12×[30+(5÷6) ] so we get 410-boys=370 boys sum =40 average of two replacing boys=20