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The cost of a square slab of concrete is proportional to the [#permalink]
21 Jul 2009, 14:28

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A

B

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D

E

Difficulty:

5% (low)

Question Stats:

57% (00:00) correct
43% (01:34) wrong based on 11 sessions

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

"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

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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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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GMAT is an addiction and I am darn addicted

Preparation for final battel: GMAT PREP-1 750 Q50 V41 - Oct 16 2011 GMAT PREP-2 710 Q50 V36 - Oct 22 2011 ==> Scored 50 in Quant second time in a row MGMAT---- -1 560 Q28 V39 - Oct 29 2011 ==> Left Quant half done and continued with Verbal. Happy to see Q39