[求助]GMAT Prep Math 一道题

DC:

 The cost of a square slab is proportional to its thickness and also proportional to the square of its length. What is the cost of a square slab that is 3 meters long and 0.1 meter thick?

(1) The cost of a square slab that is 2 meters long and 0.2 meter thick is $160 more than the cost of a square slab that is 2 meters long and 0.1 meter thick.

(2) The cost of a square slab that is 3 meters long and 0.1 meter thick is $200 more than the cost of a square slab that is 2 meter long and 0.1 meter thick.

请大牛指教！

……是不是这样子啊。

设按其厚度所算的单价为x，其长度所算的单价为y。

0.2x+2y+160=2y+0.1x

3y+0.1x+200=2y+0.1x

算出两个单价后，再用主题干里的已知数代入……所以选c?

答案是D... 我和老总的做法是一样的 搞不懂啊~ 请大牛指教！！

既然COST与长度的平方和厚度都成比例,可以列出方程,COST=A(常量)*长度的平方*厚度.

问题的C=A*0.3,也就是说求出A就可以了,选D