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The cost of a square slab is proportional to its thickness and also pr [#permalink]

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21 Jul 2009, 15:28

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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 0.1m thick.

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

(2) The cost of a square slab that is 3 meters long and 0.1 m thick is 200 more than the cost of a square slab that is 2m long and 0.1 m thick

Re: The cost of a square slab is proportional to its thickness and also pr [#permalink]

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21 Jul 2009, 16:02

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Thickness = t Length = l \(c = 9*0.1*k = ?\)

"and also proportional" means that we can put both in the same formula:

\(Cost = k*t*l^2\), where k is a constant

1) \(k*2^2*0.1\) costs x \(k*2^2*0.2\) costs x + 160 Using rule of three (cross-multiplication): \((k*2^2*0.1)/(k*2^2*0.2)= x/( x + 160 )\), you can find x, and then do the same with 9*0.1*k SUFFICIENT

Re: The cost of a square slab is proportional to its thickness and also pr [#permalink]

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20 Dec 2009, 22:32

The key with such questions is to set up the formula based on the proportionality.

Cost = K*(L^2)*T Where K is a constant L is the length T is the thickness Solving we get D

Note is something is inversely proportional, divide instead of multiply. For example if the cost is inversely proportional to the square root of slab impurity then the above formula will become Cost = K*(L^2)*T/sqrt(I)
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Re: The cost of a square slab is proportional to its thickness and also pr [#permalink]

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16 Oct 2011, 10:41

seofah wrote:

The cost of a square slab of concrete is proportional to the thickness and also proportional to the square of the length. What is the cost of square slab that is 3 meters long and 0.1 meters thick? a. 2m long by 0.2m thick is $160 more than 2m long by 0.1m thick b. 3m long by 0.1m thick is $200 more than 2m long by 0.1m thick

Got D but worked as following:

a. 2^2L + .2W = 2^2L + .1W + 160 => SUFFICIENT (Solve for W and L) b. 3^2L + .1W = 2^2L + .1W + 200 => SUFFICIENT (Solve for W and L)

Wonder if this a right approach to attack such question.
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Re: The cost of a square slab is proportional to its thickness and also pr [#permalink]

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15 Dec 2014, 07:31

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