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A welder received an order to make a 1 million liter  [#permalink]

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10
101 00:00

Difficulty:   65% (hard)

Question Stats: 63% (02:37) correct 37% (02:35) wrong based on 898 sessions

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A welder received an order to make a 1 million liter cube-shaped tank. If he has only 4x2 meter sheets of metal that can be cut, how many metal sheets will be required for this order? (1 cubic meter = 1,000 liters)

A. 92
B. 90
C. 82
D. 78
E. 75

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Originally posted by manalq8 on 16 Jan 2012, 09:59.
Last edited by Bunuel on 02 Apr 2013, 15:20, edited 2 times in total.
Renamed the topic, edited the question and added the OA.
Math Expert V
Joined: 02 Sep 2009
Posts: 59020

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10
28
manalq8 wrote:
A welder received an order to make a 1 million liter cube-shaped tank. If he has only 4x2 meter sheets of metal that can be cut, how many metal sheets will be required for this order? (1 cubic meter = 1,000 liters)

92
90
82
78
75

1 million liter cube-shaped tank = 1,000,000/1,000 = 1,000 cubic meter tank --> the cube-shaped tank with a side of 10m (10^3=1,000).

Surface area of this tank would be 6 (# of faces of a cube) * 10^2 (area of each face) = 600 m^2.

# of 4*2=8m^2 sheet needed is 600/8=75.

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##### General Discussion
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4467

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2
Hi, there! I'm happy to contribute here!

The question say: A welder received an order to make a 1 million liter cube-shaped tank. (1 cubic meter = 1,000 liters)

In other words, the tank is going to have a volume of 1000 cubic meters. That would equal 1 million liters.

A cube with a volume of 1000 cubic meters must be (10 meters) x (10 meters) x (10 meters).

The question doesn't specify whether this tank should have a closed top or an open top. (The real GMAT is good about specifying things like that.) Here, we are going to assume a closed top, only because if the top is open, we don't use enough metal --- we get an answer smaller than any of the answer choices. A closed-top cube, a full cube, has 6 sides, each of which is (10 meters) x (10 meters). That's a total surface area of 600 sq m.

The question tells us: he has only 4x2 meter sheets of metal that can be cut.

Each sheet has an area of 8 sq m. How many of these need to fill up 600 sq m? 600/8 = 75. He needs 75 sheets.

It appears that both Mr. Bunuel and I got the same answer, different from the OA you posted. Perhaps you miscopied.

Please let me know if you have any questions on this.

Mike _________________
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GMAT 1: 700 Q43 V42 GMAT 2: 730 Q47 V42 Re: A welder received an order to make a 1 million liter  [#permalink]

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1
Just raising awareness -

Looks like selecting E is resulting in a wrong answer, the GMAT club Timer is incorrectly saying that C is the correct choice.

Are others having the same issue?
Math Expert V
Joined: 02 Sep 2009
Posts: 59020
Re: A welder received an order to make a 1 million liter  [#permalink]

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FromGMATToMBA wrote:
Just raising awareness -

Looks like selecting E is resulting in a wrong answer, the GMAT club Timer is incorrectly saying that C is the correct choice.

Are others having the same issue?

Edited the OA. Thank you.
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Re: A welder received an order to make a 1 million liter  [#permalink]

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10^5 for volume in a cube implies 10^2*10^2*10^2 which means that the surface area of a side is 10^2. Well, we want to build the total surface area so if cube has 6 sides then 6*100 = 600. Since the area covered by each sheet is 8 , then we have 600/8 = 75 sheets needed

E

Let me know if this is clear
Cheers
J
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4467
Re: A welder received an order to make a 1 million liter  [#permalink]

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3
jlgdr wrote:
10^5 for volume in a cube implies 10^2*10^2*10^2 which means that the surface area of a side is 10^2. Well, we want to build the total surface area so if cube has 6 sides then 6*100 = 600. Since the area covered by each sheet is 8 , then we have 600/8 = 75 sheets needed

E

Let me know if this is clear
Cheers
J

Dear jlgdr,
Forgive me, my friend, but I am going to correct a couple of mistakes in your approach, in an attempt to strengthen your understanding as well as the understanding of anyone else who chances upon this post.

First of all, 1 million = 1,000,000 = 10^6, not 10^5.

Second, the 1 million in this problem is 1 million liters, and the liter is a unit of volume. If you say that the cube is 10^2 = 100 on each edge, then that's 100 whats? a 100 cube-roots-of-a-liter?? You see, something becomes really funky about the units here. (In fact, a liter is a cubic decimeter, that is, a cube that is 10 cm on each side, but that would put the side of the cube at 100 decimeters, a most peculiar unit to employ.)

Finally, if the cube really were (10^2)*(10^2)*(10^2), then (10^2) would be the length of an edge, and (10^2)*(10^2) = 10^4 would be the area of a face. In general, if a cube has volume L^3, it has edge-length L, and each face has an area of L^2.

Your mistakes canceled, so you wound up with the correct answer. It's very important to appreciate when you get a question correct for correct reasons, and when you get it correct for incorrect reasons.

I hope all this helps.
Mike _________________
Mike McGarry
Magoosh Test Prep

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Re: A welder received an order to make a 1 million liter  [#permalink]

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1
Volume of tank = 10^6 liters -> 10^6/10^3 cubic m = 10^3

Volume of cube = a^3 -> a = 10 m
Surface area of cube = 6a^2 = 600 squared m
Area of one sheet = 4*2 = 8 squared m

N = 600/8 = 75 (E) Re: A welder received an order to make a 1 million liter   [#permalink] 27 Mar 2019, 22:55
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