At a school camp, 30% of the students were boys. When 87 students left the camp after the second day, half the original number of boys were left behind, and the number of girls decreased by 20%. How many girls were at the camp in the beginning?

Answer 1

To start, there were b boys and g girls.

b = 3/7 g

(b+g)-87 = b/2 + 4/5 g
so,
b + 7b/3 - 87 = b/2 + (4/5)(7/3)b
b = 90
so, g = 210

check:
after 87 students left, there were 45 boys and 168 girls. 300-87 = 213 = 45+168

Answer 2

Is this Singapore Math?

Answer 3

Yes this is grade 7 Singapore math @NOYB

Answer 4

Thanks! :)