Percentage problem

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mathewmithun: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Thu Oct 08, 2009 12:02 am; Location: India

by mathewmithun » Mon Nov 14, 2011 3:12 am

Fresh watemelons contain 90% water by weight whereas dry watermelons contains 20% water by weight. what is the weight of dry watermelon obtained from 20kgs of fresh watermelon?

a: 2.4KG b: 2KG c: 2.5KG d: Cannot be determined

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Source: Beat The GMAT — Problem Solving | Mon Nov 14, 2011 3:12 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Mon Nov 14, 2011 3:20 am

I am assuming they ask for weight of pulp here.

20kg fresh has 18 kg water and 2 kg pulp.

2kg pulp in a dry water melon (80% pulp) translates = 2/0.8 = 2.5 kgs of dry water melon C IMO

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mathewmithun: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Thu Oct 08, 2009 12:02 am; Location: India

by mathewmithun » Mon Nov 14, 2011 3:24 am

shankar-you are correct...

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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Mon Nov 14, 2011 3:30 am

mathewmithun wrote:Fresh watemelons contain 90% water by weight whereas dry watermelons contains 20% water by weight. what is the weight of dry watermelon obtained from 20kgs of fresh watermelon?
a: 2.4KG b: 2KG c: 2.5KG d: Cannot be determined

Quantity of non-water component in 20 kgs of fresh watermelon = 20*(10/100) = 2 kgs
The question can be rephrased to
'What amount of dry watermelon contains 2 kgs of non-water component'

100 kgs of dry watermelon contains 80 kgs of non-water component
? kgs of dry watermelon contains 2 kgs of non-water component

100/? = 80/2 => ? = 200/80 = 2.5 kgs

IMO C

Anil Gandham
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tpr-becky: GMAT Instructor; Posts: 509; Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members; Location: Irvine, CA; Thanked: 199 times; GMAT Score:750

by tpr-becky » Mon Nov 14, 2011 2:29 pm

the trick here is to figure out how much fruit (without water) there is and then work from there.

20kg of fresh watermelon is 10% fruit so there is 2kg of fruit.

The fruit will not change, only the ratio of water to fruit. So in a dry watermelon there will be 2kg of fruit, which is 80% of the weight of a dry watermelon. So if 2kg is 80% of the weight that means that 2kg = 80/100 (dry weight) and thus it calculates to 2.5kg of dry weight so C is the answer.

Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA

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