UPSC CDS 2 2020 Math Paper

Let no of boys x and no of girls y .
So, x+y=100 …….(i)
and, the mean weight of the boys = 50 kg
⇒ total weight of boys = 50x [∵mean=

total ‌sum

no

]
and, the mean weight of the girls = 40 kg
⇒ total weight of girls = 40y
We have, the mean weight of 100 students = 46 kg
⇒

50x+40y

100

=46
⇒5x+4y=460 …….(ii)
Solving equation (i) and (ii), we get
x=60 and y=40
So, no of boys is exceed by 20 from no the girls.