There are 139 pupils in Campsite W and 317 pupils in Campsite X. Given that the number of girls in both campsites are the same and the number of boys in Campsite X is 3 times that of Campsite W, find the number of girls in both campsites.
Number of boys in Campsite W = 1 u

Number of boys in Campsite X
= 3 x 1 u
= 3 u

Number of girls in both campsites are the same.

Number of pupils in Campsite W = Girls + 1 u 
Number of pupils in Campsite X = Girls + 3 u 

Girls + 1 u = 139 --- (1)
Girls + 3 u = 317 --- (2)

(2) - (1)
3 u - 1 u = 317 - 139 
2 u = 178

1 u = 178 ÷ 2 = 89

Number of girls in Campsite W
= 139 - 1 u
= 139 - 89
= 50

Total number of girls in both campsites
= 2 x 50
= 100

Answer(s): 100