A classroom contains an equal number of boys and girls. If 9 girls​ leave, twice as many boys as girls remain. What was the original number of students​ present?

Answer 1

(g - 9) = (1/2) b
but g = b
so
2 (b-9) = b
2 b - 18 = b
b = 18
so g = 18
and total = 2*18 = 36