Question

Number of boys : Number of girls = 11 : 9

Answer 1

The first thing we are going to do for this case is define variables.
 We have then:
 x = Number of boys
 y = Number of girls
 We now write the system of equations:
 x / y = 11/9
 x = y + 124
 Solving the system we have:
 x = 682
 y = 558
 The number of students is:
 x + y = 682 + 558 = 1240
 Answer:
 the total students in the school is:
 1240 students