PREP模考DS题求指导

zjhzkingsam

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.
我选的是C，答案是D。
我的理解是由（1）可以推出cost与thick之间的比例关系，由（2）可以推出cost与length之间的比例关系，所以是C。不明白为什么选D啊啊啊啊
The cost of a square slab is proportional to its thickness and also proportional to the square of its length如何理解呢？是说Cost=a*t+b*l^2（说明：a,b是比例常数，t和l分别代表thickness和length）

youngerlee

Cost=a*t+n*l^2这里中间应该是乘啊，即：Cost=a*t * n*l^2

zjhzkingsam

哦，如果是这样就说的通了！谢谢！