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gmatmachoman: Legendary Member; Posts: 2326; Joined: Mon Jul 28, 2008 3:54 am; Thanked: 173 times; Followed by:2 members; GMAT Score:710

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by gmatmachoman » Mon May 03, 2010 4:56 am

If a% of b is c, b% of c is a and c% of a is 1, then which of the following is not true?

a. a = 10 b. b = 100 c. a = c d. a = b

OA:D

Last edited by gmatmachoman on Mon May 03, 2010 5:52 am, edited 1 time in total.

R&D on GMAT algorithm:

https://www.beatthegmat.com/r-d-on-gmat- ... tml#305739

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Source: Beat The GMAT — Problem Solving | Mon May 03, 2010 4:56 am

clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 am; Thanked: 85 times; Followed by:3 members

by clock60 » Mon May 03, 2010 5:12 am

gmatmachoman wrote:If a% of b is c, b% of c is a and c% of a is 1, then which of the following is not true?

a. a = 10 b. b = 100 c. a = c d. a = b

i got D here a=/=b, but a^2=b

ab/c=100
bc/a=100
ca=100

bc/a=ca, cancel c, and left with
b=a^2

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grockit_andrea: GMAT Instructor; Posts: 357; Joined: Wed Aug 12, 2009 8:31 pm; Thanked: 128 times; Followed by:7 members

by grockit_andrea » Mon May 03, 2010 5:17 am

I also got D; I just started plugging in the answers, beginning with A, and working my way backward in the problem from the last equation to the first one. If a is 10, then c would also be 10, because 10% of 10 is 1. b% of of c is a, so b% of 10 is 10, which makes b = 100. And just to double-check, I plugged them all into the first equation and found that 10% of 100 is indeed 10. (that is, a% of b is c). Based on that, all of the choices are true besides D.

If you don't know where to start on a problem, working backwards from the answers can be really helpful.

Andrea A.
Grockit Tutor
https://www.grockit.com