
Nathaniel B. answered 04/12/15
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In September, 20% of 1200 students were boys. That means that .2 * 1200 students or 240 students were boys. We need to know how many more students we should add to give us 25% boys.
We can use the following steps:
let x=number boys enrolled in October
(240+x)/(1200+x)=.25
240+x=300+.25x
60=.75x
x=80
So 80 boys enrolled in October
Check: we said 80 enrolled, so 320 boys altogether; 320/1280=25% This checks.