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What is the sum of a, b and c?

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Source: — Data Sufficiency |
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Re: What is the sum of a, b and c?

by Stuart@KaplanGMAT » Fri Jan 02, 2009 2:08 am
vittalgmat wrote:What is the sum of a, b, and c?

1. a:b:c = 3:4:7
2. c - a = 12

Pls explain

thanks
Q: a+b+c = ?

(1) from a ratio, we can't determine any exact numbers: insufficient.
(2) no info about b: insufficient.

Together:

From (1), we know that a/c = 3/7. From (2), we know that c = a + 12. Combined, we know that a/a+12 = 3/7. We can solve this equation for a, then use the ratio to solve for both b and c: sufficient.

Together sufficient, apart insufficient: choose (C).
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by maihuna » Fri Jan 02, 2009 2:37 am
There is a simpler way doing that:

1. a:b:c = 3:4:7
2. c - a = 12

we know c = 7x a = 3x so c-a = 4x = 12 = > x = 3

so the numers are 3x 4x 7x i.e. 9 12 21 and so a powerful scientfic calculator can be used to determine a + b + c

and so CCCCCCCCCCCCC
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by vittalgmat » Fri Jan 02, 2009 2:53 am
Silly me!!!. I was very close to the answer :(


Thanks Stuart and Maihuna for excellent explanation.
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