how to solve this type of question??

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alivapriyada: Master | Next Rank: 500 Posts; Posts: 146; Joined: Fri Jun 25, 2010 3:42 amFollowed by: 1 member; Thanked: 3 times; GMAT Score:560

by alivapriyada » Sat Jul 10, 2010 7:56 am

A forty gallons of gas is required to travel 400 miles using a 1200 CC engine. If the capacity of the engine is directly varying with the volume of gas, then how many gallons of gas required to travel 600 miles using 1500 CC engine?
A) 20
B) 27.5
C) 37.5
D) 42.5
E) 75

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Source: Beat The GMAT — Problem Solving | Sat Jul 10, 2010 7:56 am

4GMAT_Mumbai: Master | Next Rank: 500 Posts; Posts: 161; Joined: Mon Apr 05, 2010 9:06 am; Location: Mumbai; Thanked: 37 times

by 4GMAT_Mumbai » Sat Jul 10, 2010 8:09 am

Hi,

This is a proportions based question.

40 gallons of gas r required to travel 400 miles using 1200 CC engine.

Change the parameters one by one.

40 * 1.5 (=60 gallons) gallons of gas r required to travel 600 miles using 1200 CC engine. (Why? because 600 = 400 * 1.5)

60 / 4 (=15) gallons of gas r required to travel 600 miles using 300 CC engine.

Why? because 300 = 1200 / 4.

Why 300? because 300 is the HCF of 1200 and 1500.

15 * 5 (=75) gallons of gas r required to travel 600 miles using 1500 CC engine.

Hope this helps. Thanks.

Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai

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alivapriyada: Master | Next Rank: 500 Posts; Posts: 146; Joined: Fri Jun 25, 2010 3:42 amFollowed by: 1 member; Thanked: 3 times; GMAT Score:560

by alivapriyada » Sat Jul 10, 2010 8:14 am

I am really thankful for your well explained reply dear but the OA is 42.5.And that is what confusing me.

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IAN_DUDLA: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Thu Dec 24, 2009 7:42 am

by IAN_DUDLA » Sat Jul 10, 2010 9:45 am

if it takes 60 gallons of gas to travel 600 miles running on a 1200 cc engine (400m/600m=40g/x), it is impossible to burn less gas (i.e. 42.5) running on an engine even with a greater capacity.

alivapriyada, you have to check your source.

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outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members; Thanked: 46 times

by outreach » Sat Jul 10, 2010 10:53 am

C-capacity
V-volume of gas ...
k-constant
C=kV =>1200= k*40= >k=30

Now,
1500= 30 *V => V=50
2nd engine requires 50 gallons for same 400 miles
so it should require 75 gallons for 600 miles

E

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