If 160 kg of dry wood pulp is needed to produce 50 sheets of

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gmat_guy666: Senior | Next Rank: 100 Posts; Posts: 48; Joined: Tue Apr 23, 2013 12:51 am; Thanked: 6 times

by gmat_guy666 » Tue Aug 26, 2014 4:21 am

If 160 kg of dry wood pulp is needed to produce 50 sheets of paper, how much raw pulp will be needed to produce 200 sheets of paper if raw pulp loses 20 percent of its weight during desiccation?

A)400
B)600
C)640
D)800
E)850

OA D

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Source: Beat The GMAT — Problem Solving | Tue Aug 26, 2014 4:21 am

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Tue Aug 26, 2014 4:34 am

gmat_guy666 wrote:If 160 kg of dry wood pulp is needed to produce 50 sheets of paper, how much raw pulp will be needed to produce 200 sheets of paper if raw pulp loses 20 percent of its weight during desiccation?

A)400
B)600
C)640
D)800
E)850

50 sheets of paper are yielded by 160kg of dry pulp.
Thus, 200 sheets of paper -- 4 times the number of sheets -- will be produced by 4 times the amount of dry pulp:
4*160 = 640kg.

We can PLUG IN THE ANSWERS, which represent the required amount of RAW pulp.
When the correct answer choice loses 20% of its weight during desiccation, the result will be 640kg of dry pulp.
To yield 640kg of dry pulp, the amount of raw pulp must be greater than 640.
Eliminate A, B and C.

Answer choice D: 800
After 20% is lost during desiccation, the amount of dry pulp = 800 - 20% of 800 = 800 - 160 = 640.
Success!

The correct answer is D.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Aug 26, 2014 9:13 am

gmat_guy666 wrote:If 160 kg of DRY wood pulp is needed to produce 50 sheets of paper, how much RAW pulp will be needed to produce 200 sheets of paper if RAW pulp loses 20 percent of its weight during desiccation?

A)400
B)600
C)640
D)800
E)850

Another approach.

Raw (i.e., WET) pulp loses 20 percent of its weight during desiccation (drying process)
In other words, RAW pulp is 20% water.
This means that RAW pulp is 80% DRY wood pulp.
So, for example, 100 kg of RAW pulp will produce 80 kg of DRY pulp (and 20 kg of water).
It also means that 200 kg of RAW pulp will produce 160 kg of DRY pulp.

Aside: I made this observation, because the question tells us that 160 kg of DRY wood pulp is needed to produce 50 sheets of paper

So, 200 kg of RAW pulp produces 160 kg of DRY pulp, which produces 50 sheets of paper.

We want 200 sheets of paper, so, we'll need 4 TIMES as much pulp.

So, 800 kg of RAW pulp produces 640 kg of DRY pulp, which produces 200 sheets of paper.

Answer: D

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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