In school, the ratio of boys to girls is 9:4 if there are presently 720 girl students, how many more girls would it take to reduce the ratio of boys to girls to 2:1
total = (9/4) 720 + 720 = 2340
and (9/4)720 = 1620 boys for 720 girls
new total =2340 + g
new girls = 720 + g
boys / new girls = 2 = 1620 / (720+g)
1440 + 2 g = 1620
2 g = 180
g = 90
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check
720 + 90 = 810 girls now
boys = (9/4) 720 = 1620
good