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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]

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New post 26 Nov 2010, 10:57
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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
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Re: Is it a hard question  [#permalink]

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New post 26 Nov 2010, 11:18
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: If each of a, b and c is positive, and a = 5b + 7c, what is  [#permalink]

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New post 18 Sep 2016, 20:31
B is correct. Here's why:

(1) 2b +5c = 50

NOT SUFFICIENT - we don't have any way to get a/b

(2) c = 3b - 5c --> Simplifies to 6c = 3b --> b = 2c

We know from the beginning of the question that a = 5b+7c --> Plug b = 2c and you arrive at a = 17c

Thus a/b = 17/2
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Re: If each of a, b and c is positive, and a = 5b + 7c, what is  [#permalink]

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New post 05 Jan 2019, 05:54
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Re: If each of a, b and c is positive, and a = 5b + 7c, what is   [#permalink] 05 Jan 2019, 05:54
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