In a class of 50 students. 40% are girls. The average weight of the boys is 62 kg and that of the girls is 58 kg. What is the average weight (in kg) of the whole class?

The total number of students in the class is $$50$$.

Percentage of girls = $$40\%$$. Therefore,
number of girls = $$40\% \times 50 = 0.40 \times 50 = 20$$.

Since there are $$50$$ students in all, the remaining students are boys:
number of boys = $$50 - 20 = 30$$.

Average weight of the boys = $$62 \text{ kg}$$.
Total weight of the boys = $$30 \times 62 = 1860 \text{ kg}$$.

Average weight of the girls = $$58 \text{ kg}$$.
Total weight of the girls = $$20 \times 58 = 1160 \text{ kg}$$.

Total weight of the whole class = $$1860 + 1160 = 3020 \text{ kg}$$.

Average weight of the whole class = $$\frac{\text{Total weight}}{\text{Total students}} = \frac{3020}{50} = 60.4 \text{ kg}$$.

Hence the average weight of the class is $$60.4 \text{ kg}$$.
Option A which is: 60.4.