Question 981206

In a school, there are 12% girls. If 5boys and 15girls are newly admitted to the school, the percentage of girls becomes 15. What is the total strength of the school? Z
<pre>Let number of students in school be S
If originally there were 12% girls, then original number of girls was: .12S
After addition of 15 girls, new number of girls = .12S + 15
New number of students: S + 5 + 15, or S + 20
Equation to form: {{{New_number_of_girls/New_number_of_students = New_percentage_of_girls}}}
This translates to: {{{(.12S + 15)/(S + 20) = .15}}}
 .15(S + 20) = .12S + 15 -------- Cross-multiplying
    .15S + 3 = .12S + 15
 .15S - .12S = 15 - 3
        .03S = 12
S, or original number of students = {{{12/.03}}}, or {{{highlight_green(400)}}}