Answer:11
Explanation:
Boys : girls=7:1
Sum of ratio=7+1=8
Let number of girls be y
Then number of boys=y+66
Total number of pupils=y+y+66
Total number of pupils=2y+66
girls only=(girl ratio)/(sum of ratio) x (total number of pupils)
y=1/8 x (2y+66)
Cross multiply
y x 8=2y + 66
8y=2y + 66
Collect like terms
8y-2y=66
6y=66
Divide both sides by 6
6y/6=66/6
y=11
There are 11 girls