一道PREP 数学，马上考试，急

cicijinlan · 发表于 2010-10-25 20:47:46

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 meters thick is $160 more than the cost of a square slab that is 2 meters long and 0.1 meters thick.
(2). the cost of a square slab that is 3 meters long and 0.1 meters thick is $200 more than the cost of a square slab that is 2 meters long and 0.1 meters thick.
答案是D。。。为什么啊，可是单独的不是都消掉了吗？我选的C。
恳请大家帮忙解答，谢谢

serenashu · 发表于 2010-10-25 20:49:14

我也想问这题，当初我也选的C，最后也不是很明白~~~~~

knightshield · 发表于 2010-10-25 21:04:38

题目转换成数学：cost=a*thickness*b*length^2
要求：a*0.1*b*9,所以知道ab就行了。
(1) a*0.2*b*4=160+a*0.1*b*4 可求ab，sufficient. (2)同理

cicijinlan · 发表于 2010-10-25 21:12:09

题目转换成数学：cost=a*thickness*b*length^2
要求：a*0.1*b*9,所以知道ab就行了。
(1) a*0.2*b*4=160+a*0.1*b*4 可求ab，sufficient. (2)同理

-- by 会员 knightshield (2010/10/25 21:04:38)

哦，对~傻了，我想成要相加的了~谢谢

一道PREP 数学，马上考试，急

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