求助 prep ds 1---214

lxw19 · 发表于 2010-10-7 16:09:02

214.20789-!-item-!-187;#058&013258

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.

这道题选的D 看答案看得晕得很~~有没有哪位大牛简单的解释一下思路呢？The cost of a square slab is proportional to its thickness and also proportional to the square of its length.这个条件应该怎么用呢？

shawnxlee · 发表于 2010-10-7 17:17:31

214.20789-!-item-!-187;#058&013258
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.
这道题选的D 看答案看得晕得很~~有没有哪位大牛简单的解释一下思路呢？The cost of a square slab is proportional to its thickness and also proportional to the square of its length.这个条件应该怎么用呢？
-- by 会员 lxw19 (2010/10/7 16:09:02)

The cost of a square slab is proportional to its thickness and also proportional to the square of its length.这个条件应该怎么用呢？
这句话理解为cost与这个板子length的平方成正比，于是综合可列下面的等式。
设cost为C, length为R, 厚度为T, 则C=KR^2T, 在此K为常数。
由(1)可得两个关于K的方程式，解出K的值，最后得问题C=K*3^2*0.1
同理由(2)可解出K，带出也可以得到C的值

lxw19 · 发表于 2010-10-7 18:40:19

嗯明了了~~谢谢ls

求助 prep ds 1---214

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