Concrete slabs

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Concrete slabs

by Woozler » Wed Dec 08, 2010 2:49 pm
The cost of a square concrete 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 meters thick?

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

Edit: corrected
Last edited by Woozler on Wed Dec 08, 2010 3:21 pm, edited 1 time in total.

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by Bharat » Wed Dec 08, 2010 3:16 pm
Hi Woozler,
It appears that there is some typographical error in statement 1: "....quare slab 2 meters long and 0.2 m long...." (both are lengths?)

Otherwise the difference in price of two slabs is sufficient to answer the question. So statement 2 alone is sufficient here.
Regards,
Bharat

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by Woozler » Wed Dec 08, 2010 3:22 pm
Could you explain why it is sufficient? I am not really sure how we can go from "$160 more" to "this is the cost of the slab"

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by Bharat » Wed Dec 08, 2010 3:45 pm
Hi Woozler,
As per given information: cost = k*t*(l^2). (here is k is a proportional constant).
from #2: 160 = k*0.2*(2^2) - k*0.1*(2^2)
from here we can solve for k.
Put k back in cost formula & plug in t = 0.1, l = 3 to get the cost.

Let me know if you have further questions.
Regards,
Bharat.

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by Woozler » Wed Dec 08, 2010 5:07 pm
Ah, thanks. I'm not very familiar with the idea of proportional costs/ratios/whatever. Didn't know that.