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If each of a, b and c is positive, and a = 5b + 7c, what is

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If each of a, b and c is positive, and a = 5b + 7c, what is [#permalink] New post 26 Nov 2010, 09:57
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If each of a, b and c is positive, and a = 5b + 7c, what is the value of a/b?

1) 2b + 5c = 50
2) 3b - 5c = c
[Reveal] Spoiler: OA
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Re: Is it a hard question [#permalink] New post 26 Nov 2010, 10:18
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chiragatara wrote:
If each of a, b and c is positive, and a = 5b + 7c, what is the value of a/b?

1) 2b + 5c = 50
2) 3b - 5c = c


Given: a=5b+7c.

Now, as we are asked to get the value of \frac{a}{b} then divide both parts of a=5b+7c by b (to have LHS equal to \frac{a}{b}): \frac{a}{b}=5+7\frac{c}{b}. So, basically finding the value of \frac{c}{b} will be sufficient.

(1) 2b + 5c = 50 --> we can neither solve for unknowns (2 distinct linear equations, 3 variables) nor get the desired ratio. Not sufficient.
(2) 3b - 5c = c --> 3b=6c --> \frac{c}{b}=\frac{1}{2}. Sufficient.

Answer: B.
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Re: Is it a hard question   [#permalink] 26 Nov 2010, 10:18
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If each of a, b and c is positive, and a = 5b + 7c, what is

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