There are some students and girls in the library, 10 people left the library, the number of boys is three times that of girls, and six boys are leaving.
Suppose there are x girls at the beginning and y boys at the beginning.
y- 10=x÷2
y- 10=5(x-9)
X ÷ 2 = 5 (x-9)
X = 10 and Y = 15 are obtained.
So the library initially had 15 boys and 10 girls.