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mike22629: Master | Next Rank: 500 Posts; Posts: 322; Joined: Fri Mar 27, 2009 3:56 pm; Thanked: 24 times; GMAT Score:710

by mike22629 » Sat May 09, 2009 9:12 am

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 slab that is 3 meters long and .1 meter thick?

A.) the cost of a slab that is 2 meters long and .2 meters thick is $160 more than the cost of a slab that is 2 meters long and .1 meters thick

B.) the cost of a slab that is 3 meters long and .1 meters thick is $200 more than the cost of a square slab that is 2 meters long and .1 meters thick

OA after a few responses.

Source: Beat The GMAT — Data Sufficiency | Sat May 09, 2009 9:12 am

aj5105: Legendary Member; Posts: 1169; Joined: Sun Jul 06, 2008 2:34 amFollowed by: 1 member; Thanked: 25 times

by aj5105 » Sat May 09, 2009 10:56 am

I am just guessing here..

Using the formula of TSA : 2(lw + wh + hl)

(D)

mike22629: Master | Next Rank: 500 Posts; Posts: 322; Joined: Fri Mar 27, 2009 3:56 pm; Thanked: 24 times; GMAT Score:710

by mike22629 » Sat May 09, 2009 12:28 pm

That is correct. I would appreciate if someone could elaborate.

lilu: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Dec 10, 2008 5:13 pm; Location: SF, CA; Thanked: 12 times

by lilu » Sat May 09, 2009 12:57 pm

The question tells you that C=k*t*l^2
Where C=cost, k=coefficient of proportionality (what you need to find), t-thickness,l-length.

So, 1. tells us that k*0.2*4 - k*0.1*4 = 160------> k = 400
Using this information we can find the Cost of the slab in the original q--->
C=400*0.1*9 = 360

Same goes for 2. ----> k*0.1*9 - k*0.1*4 = 200----> k = 400
Answer to question c = 400*0.1*9 = 360

This is why our answer is D

The more you look, the more you see.

mike22629: Master | Next Rank: 500 Posts; Posts: 322; Joined: Fri Mar 27, 2009 3:56 pm; Thanked: 24 times; GMAT Score:710

by mike22629 » Sat May 09, 2009 5:40 pm

Thanks lilu! Great Explanation.

kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

Re: GMAT Prep

by kanha81 » Tue May 12, 2009 10:29 am

mike22629 wrote: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 slab that is 3 meters long and .1 meter thick?

A.) the cost of a slab that is 2 meters long and .2 meters thick is $160 more than the cost of a slab that is 2 meters long and .1 meters thick

B.) the cost of a slab that is 3 meters long and .1 meters thick is $200 more than the cost of a square slab that is 2 meters long and .1 meters thick

OA after a few responses.

Nice question, but can please write "0.1" instead of ".1". I am pretty sure GMAT respects the decimal by placing "0" in front of decimal.

c = k * s * t^2, where k = constant, s = length, t = thickness
c = ?, when s=3, t=0.1

(i) c=k * (2) * (0.2)^2 = 0.08 * k
c=k * (2) * (0.1)^2 = 0.02 * k

(0.08 * k) - (0.02 * k) = 160
0.06 * k = 160
k = 160 * 100 / 6

Subst. value of k in -
Suff

(ii) Same as (i) with diff. values.
Suff.

Hence [spoiler][D][/spoiler]

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