Ina class of 60 students, 40% are girls. The average weight of the whole class is 59.2 kg and the average weight of the girls is 55 kg. What is the average weight of the boys?

Let the total weight of the girls are $$=w_1$$ and the total weight of the girls are $$=w_2$$

Given that the total number of student $$=60$$

and total number of girls $$=40\%$$of total number of student$$=\dfrac{40\times 60}{100}=24$$ girls

Hence, total number of boy $$=60-24=36$$Kg

The average weight of total student $$\dfrac{w_1+w_2}{60}=59.2$$Kg

$$\Rightarrow w_1+w_2=59.2\times 60$$Kg -----------(i)

Average weight of girls $$\dfrac{w_1}{24}=55$$Kg

$$\Rightarrow w_1=55\times 24$$Kg--------------------(ii)

Now, from equation (i) and (ii)

$$\Rightarrow 55\times24+w_2=59.2\times 60$$Kg

$$\Rightarrow w_2=59.2\times 60-55\times24$$Kg

$$\Rightarrow w_2=3552-1320$$Kg

$$\Rightarrow w_2=2232$$Kg

So, average weight of the girls $$=\dfrac{2232}{36}=62$$Kg