In a class of 60 students, 40% are girls. The average weight of the boys is 62kg and that of the girls is 55kg. What is the average weight of the whole class?

Let the Weight of n girls=x and weight of m boys =y

As per the question, $$n=60\times \dfrac{40}{100}=24$$

Given that $$m+n=60$$

$$m=60-24=36$$

Average weight of boys $$\dfrac{y}{36}=62$$Kg

$$\Rightarrow y=62\times 36$$

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

$$\Rightarrow x=55\times 24$$

So, average weight of whole classes $$=\dfrac{x+y}{m+n}=\dfrac{62\times 36 +55\times 24}{24+36} $$

$$\Rightarrow \dfrac{2232+1320}{24+36}=\dfrac{3553}{60}=59.2$$Kg