In a class, the total number of boys and girls is 90. The number of boys is 10 more than the number of girls.In a test, the average score of boys is 30% more than that of girls. If the average score ofall the boys andgirls is 63, then what is the average score of girls?

Correct option is A

Given :

Total number of students = 90
Number of boys is 10 more than number of girls

Formula Used :
​$$\text{Combined Average} = \frac{(n_1 \times A_1) + (n_2 \times A_2)}{n_1 + n_2}$$​​
Solution :

Let number of girls = g
Number of boys = g + 10

g + (g + 10) = 90

2g = 80

g = 40

So,
Girls = 40
Boys = 50

Let average score of girls = x

Average score of boys = (30%) more than girls
= 1.3x

Total average = 63

​$$\frac{40x + 50(1.3x)}{90}$$​= 63

40x + 65x = 5670

105x = 5670

x = 54
Average score of girls = 54