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Intern  Joined: 12 Aug 2010
Posts: 13
If each of a, b and c is positive, and a = 5b + 7c, what is  [#permalink]

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1
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Difficulty:   55% (hard)

Question Stats: 64% (01:59) correct 36% (02:02) wrong based on 142 sessions

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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
Math Expert V
Joined: 02 Sep 2009
Posts: 57199
Re: Is it a hard question  [#permalink]

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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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Current Student 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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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
Non-Human User Joined: 09 Sep 2013
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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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_________________ 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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