b = boys g = girls
.................................
b + g = 195 b = 195 - g
b = 8
g 7
Substitute b for 195 - g in the 2nd equation:
b = 8
g 7
195 - g = 8
g 7
Cross Multiply
8g = 7 . ( 195 - g )
8g = 1365 - 7g
8g + 7g = 1365
15g = 1365
g = 1365
15
g = 91
Substitute g for 91 in one of the equations:
b + g = 195
b + 91 = 195
b = 195 - 91
b = 104
S = 104 boys.