【求助】proportional的问题

RayeRach

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 meters long and 0.1 meter thick

我的问题是这道题该怎样列式呢？
是c=k*T*L^2(k是比例）然后将（1）（2）的数代入
还是c=k1*T
      c=k2*L^2(k1 k2是不同比例）

这道题其实无需算数，但这两种方法算出的数不一样，我想问一下大家哪种列式更科学呢？
be proportional to翻译成“成比例”对吗？这种题需要关注成多大比例吗？还是简单理解为成正比而不需理会具体比例呢？

谢谢大家！

yzg1236

其实不用列式啊，但是如果你一定要列式，根据题意，你列的第二种是对的
题中说 “proportional to T and also proportional to L” 意思就是 cost 既和 T 成比例 又和 L的平方 成比例

A 和 B 成比例的意思就是

如果 A变成 N倍的A 那么B 一定也变成 N倍的B

RayeRach

谢谢！

quill

LZ列的第一个式子是对的。第二个式子表示cost只和length或者只和thickness相关，明显与题意不符。相关讨论在这个贴子里也解释得很详尽
http://www.manhattangmat.com/forums/the-cost-of-a-square-slab-is-proportional-to-thickness-t857.html