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# M07-10

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Math Expert
Joined: 02 Sep 2009
Posts: 51100

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15 Sep 2014, 23:34
3
16
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Difficulty:

65% (hard)

Question Stats:

65% (01:25) correct 35% (02:13) wrong based on 157 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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Math Expert
Joined: 02 Sep 2009
Posts: 51100

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15 Sep 2014, 23:34
3
5
Official Solution:

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

1 million liter cube-shaped tank $$= \frac{1,000,000}{1,000} = 1,000$$ cubic meter tank, which means that we have the cube-shaped tank with a side of $$10m$$ ($$10^3=1,000$$).

Surface area of this tank would be $$6 \text{ (number of faces of a cube)} * 10^2 \text{ (area of each face)} = 600$$ $$m^2$$.

Number of $$4*2=8$$ $$m^2$$ sheets needed is $$\frac{600}{8}=75$$.

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Joined: 19 Sep 2014
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21 Sep 2015, 10:30
1
Why does the tank need a cover? This confused me while answering the question. It would be good to make it clear that the tank needs a cover. For a cube-shaped tank that needs to contain 1 million liter only 62.5 sheets are necessary: we need 1 bottom and 4 sides with a required total of 500 square meter. 500/8=62.5. Edit: That would be 63 sheets
Intern
Joined: 22 Dec 2014
Posts: 1
Concentration: Finance, Economics
Schools: CBS '18
WE: Engineering (Consulting)

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21 Dec 2015, 06:53
Since 63 is not an option there, you must consider tanks with covers.
Verbal Forum Moderator
Joined: 15 Apr 2013
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Location: India
Concentration: General Management, Marketing
GMAT Date: 11-23-2015
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26 Dec 2015, 22:03
Hello,

Well the explanation is clear and concise.

I attempted the question with a 3D structure in mind.

Firstly we have a side of cube: 10 m

Secondly now how you could arrange 4 X 2 sheets in a 10 m side.

Interestingly if you draw the sheets in 10 X 10 side, you would only be able to put 12 such sheets in it with area of 2 X 2 remaining (I would try to draw it some other time): 12 X 6 = 72 sheets

Now as there are six sheets (in total) for the cube, so a total of 3 more sheets required to join adjacent sides.

This method took a little bit time to apply.

Thx
Intern
Joined: 23 Feb 2015
Posts: 2

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16 Mar 2016, 14:29
Hi Bunuel,

the sheets of metal shouldn't be in m^2? instead of meter, or the word "sheet" should already refer to a surface.

thanks
M
Manager
Joined: 19 Jan 2016
Posts: 72
Location: India
Concentration: Strategy

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24 Apr 2016, 02:14
Skytail wrote:
Why does the tank need a cover? This confused me while answering the question. It would be good to make it clear that the tank needs a cover. For a cube-shaped tank that needs to contain 1 million liter only 62.5 sheets are necessary: we need 1 bottom and 4 sides with a required total of 500 square meter. 500/8=62.5. Edit: That would be 63 sheets

Can someone explain this concept?
Intern
Joined: 25 Jun 2013
Posts: 10

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23 Jun 2016, 16:11
why do you divide 1,000,000 / 1000 to get the 1000 cubic meter tank? isn't 1,000,000 already the volume of the tank?

I got the answer 7500 because I didn't divide the 1000 at the beginning.
Math Expert
Joined: 02 Aug 2009
Posts: 7099

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23 Jun 2016, 19:37
1
glochou wrote:
why do you divide 1,000,000 / 1000 to get the 1000 cubic meter tank? isn't 1,000,000 already the volume of the tank?

I got the answer 7500 because I didn't divide the 1000 at the beginning.

Hi,

the VOLUME of liquid inside is in LITER, but we cannot have the volume of TANK also in same units..
so we require to change liters to cubic meter..

and it is given in the Q that 1 cubic meter = 1000 liters........ so 75000 liters = 75 cubic meter
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Intern
Joined: 22 Dec 2015
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19 Aug 2016, 09:29
Is there a typo in the question? Because if not, then wouldn't we also be able to use 90 sheets of metal (60 in 4x2, and 30 in 2x2, with 15 sheets of metal per side 4x2x10 and 2x2x5) ?
Senior Manager
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Location: India
Concentration: Operations, Finance
GMAT 1: 670 Q48 V34
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20 Aug 2016, 03:46
I think this is a high-quality question and I agree with explanation.
Manager
Joined: 03 Dec 2013
Posts: 70
Location: United States (HI)
GMAT 1: 660 Q49 V30
GPA: 3.56

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22 Aug 2016, 10:17
I think this is a high-quality question and I agree with explanation.
Intern
Joined: 19 Nov 2012
Posts: 29

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07 Feb 2018, 01:27
Thanks chetan2u!
Intern
Joined: 03 Sep 2017
Posts: 15
Location: Brazil
GMAT 1: 730 Q49 V41

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03 Mar 2018, 14:44
atturhari wrote:
Skytail wrote:
Why does the tank need a cover? This confused me while answering the question. It would be good to make it clear that the tank needs a cover. For a cube-shaped tank that needs to contain 1 million liter only 62.5 sheets are necessary: we need 1 bottom and 4 sides with a required total of 500 square meter. 500/8=62.5. Edit: That would be 63 sheets

Can someone explain this concept?

I also did not understand.
Why do we need to consider it with the cover?
Math Expert
Joined: 02 Sep 2009
Posts: 51100

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04 Mar 2018, 05:43
vitorcbarbieri wrote:
atturhari wrote:
Skytail wrote:
Why does the tank need a cover? This confused me while answering the question. It would be good to make it clear that the tank needs a cover. For a cube-shaped tank that needs to contain 1 million liter only 62.5 sheets are necessary: we need 1 bottom and 4 sides with a required total of 500 square meter. 500/8=62.5. Edit: That would be 63 sheets

Can someone explain this concept?

I also did not understand.
Why do we need to consider it with the cover?

Please check here: https://gmatclub.com/forum/a-welder-rec ... 26154.html

Hope it helps.
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Joined: 14 Nov 2018
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23 Nov 2018, 17:24
I think this is a poor-quality question and I agree with explanation. There are a lot of information not included in this question. For example, do we need to ensure that the 4x2 sheets will fit on one face of the tank or are they allowed to bend around the corners? also, is one layer of sheet metal acceptable? Or will we need to do an inside and outside layer? There won't be a door to this tank or any kind of opening, such as in the top of the tank?
Re M07-10 &nbs [#permalink] 23 Nov 2018, 17:24
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# M07-10

Moderators: chetan2u, Bunuel

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