一道英文数学难题!火速回答!Class A and class B have the same number of st

Let the number of girls in class A be X.
Let the number of boys in class B be Y.
Initially,X / Y = 3 / 2
Y = 3X/ 2
Let the number of girls in class B be x.
Let the number of girl in class B be y.
Initially,y / x = 2
y = 2x
X + Y = x + y
X + 3X/2 = x + 2x
5/2 X = 3 x
After one girl in class A is replaced by one boy in class B
(X - 1) / (Y + 1) = (x + 1) / (y - 1) --> multiple both side by (Y + 1)(y - 1)
(X - 1)(y - 1) = (x + 1) (Y + 1)
Express y and Y in terms of X
(X - 1)(2x - 1) = (x + 1) (3X/2 + 1)
2Xx - X - 2x + 1 = 3/2 * Xx + x + 3/2 * X + 1
1/2 * Xx - 5/2 X - 3x = 0
Since 5/2 X = 3 x
1/2 * Xx - 3x - 3x = 0
Xx - 6x = 0
Since X = 6x/5
6x/5 * x - 6x = 0
6x*x - 30x = 0
x (6x - 30) = 0
x = 0 OR 6x = 30
x = 5
y = 2x y = 10
X = 6x/5 = 6
Y = 3X/ 2 = 9
过程绝对不应该这么复杂 >.< 不过答案似乎正确.