prep 数学ds一道，谢谢

158.       15958-!-item-!-187;#058&010868

A store purchased 20 coats that each cost an equal amount and then sold each of the 20 coats at an equal price.  What was the store's gross profit on the 20 coats?

(1)  If the selling price per coat had been twice as much, the store's gross profit on the 20 coats would have been $2,400.

(2)  If the selling price per coat had been $2 more, the store's gross profit on the 20 coats would have been $440.

答案是B，百思不得其解啊。感觉单独的B求不出来啊

设，20件外套的买入价为x,卖出价为y。gross profit=20(y-x)

1、根据条件，可以得出y=2x，代入上式得，gross profit=20(2x-x)=20x,因为x为未知数，无法判断gross profit是否等于2400

2、根据条件，可以得出y=2+x，带入上式得，gross profit=20(2+x-x)=40……不对啊，兄台，你的第二个条件怎么会是440？？是不是打错了……

(1)If the selling price per coat had been twice as much,的意思不是Y=2x吧，是指本身Y增加到2Y吧

(2)  If the selling price per coat had been $2 more,的意思是指Y增加到了Y+2吧

但如果按我这样理解，要两个条件一起才可以，还是得不出B,所以求大家帮忙下了。数字应该是对的。

哦明白了