Number of boys: number of girls=11: 9there are 124 boys more than girls. what is the total number of student at the school?

boys (b): g + 124

girls (g): g

Total (T): b + g

I am going to set up a proportion based on boys to total students.

⇒  

⇒ 11(124 + 2g) = 20(124 + g)

⇒ 1364 + 22g = 2480 + 20g

⇒ 1364  + 2g = 2480

⇒              2g = 1116

⇒                g = 558

boys (b): g + 124   = (558) + 124   = 682

Total (T): b + g   = 682 + 558   = 1240

1240 total students

distance covered by pamela in 9 l of fuel = 99km

let us apply unitary method here.

distance covered by pamela in 1 l of fuel =99/9 =11 km

now let us find distance covered by pamela if she has 12 l of fuel.

distance covered in 12 l = distance covered in 1 l of fuel * 12

we know that distance covered by here in 1 l is 11 km.

so distance covered in 12 l of fuel = 11*12 = 132 km.