Difficult Math Question #34 - Arithmetic - The Beat The GMAT Forum

Difficult Math Question #34 - Arithmetic

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800guy: Master | Next Rank: 500 Posts; Posts: 354; Joined: Tue Jun 27, 2006 9:20 pmFollowed by: 5 members; Thanked: 11 times

by 800guy » Wed Oct 25, 2006 3:30 pm

Two numbers are less than a third number by 30% and 37 % respectively. How much percent is the second number less than the first?

a) 10 % b) 7 % c) 4 % d) 3 %

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Source: Beat The GMAT — Problem Solving | Wed Oct 25, 2006 3:30 pm

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Wed Oct 25, 2006 11:05 pm

Two numbers are less than a third number by 30% and 37 % respectively. How much percent is the second number less than the first?

a) 10 % b) 7 % c) 4 % d) 3 %

A is the answer ..

say the original no is X
first no: is .7X
second no: is .63X

it is (.7-.63) X/.7 =.1 =10%

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rajs.kumar: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Fri Jun 09, 2006 2:47 am; Thanked: 2 times

by rajs.kumar » Thu Oct 26, 2006 2:14 am

agree with ajith.

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800guy: Master | Next Rank: 500 Posts; Posts: 354; Joined: Tue Jun 27, 2006 9:20 pmFollowed by: 5 members; Thanked: 11 times

OA

by 800guy » Fri Oct 27, 2006 3:08 pm

here's the OA:

.7 & .63

diff in %= (.7 - .63)/.7 * 100= .07/.7 * 100= 10%

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navdeepbajwa: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Sun Aug 02, 2009 9:10 pmFollowed by: 1 member; Thanked: 1 times

please explain

by navdeepbajwa » Tue Oct 20, 2009 1:01 am

I can't understand this part

diff in %= (.7 - .63)/.7 * 100

why we have to divide by 0.7 why can't it be difference * 100 = 7%

thanks

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regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

Re: please explain

by regor60 » Tue Oct 20, 2009 9:12 am

navdeepbajwa wrote:I can't understand this part

diff in %= (.7 - .63)/.7 * 100

why we have to divide by 0.7 why can't it be difference * 100 = 7%

thanks

Keep track of the base.

The difference of 7% is referenced to the "third" number. 10% is the difference referenced to the "first" number, which itself is 70% of the "third" number. The question is asking for the difference referenced to the "first" number.

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