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If a and b are positive integers, what is the value of a + b

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Director
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If a and b are positive integers, what is the value of a + b [#permalink]  30 Nov 2005, 09:51
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If $$a$$ and $$b$$ are positive integers, what is the value of $$a + b$$?

$$1) \hspace{4} \frac{a}{b} = \frac{5}{8}$$

2) the greatest common divisor of a and b is 1
[Reveal] Spoiler: OA

Last edited by fluke on 19 Jul 2011, 06:53, edited 1 time in total.
Corrected the question
SVP
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Re: DS integers [#permalink]  30 Nov 2005, 10:28
joemama142000 wrote:
If a and b are positive integers, what is the value of a + b?

1) a/b = 5/b

2) the greatest comon divisor of a and b is 1

since a and b are positive integers----> they're not 0
1. ---->a=5 , how about b? -->insuff
2. 3 and 5, 5 and 7, yields different sums ----->insuff

1 and 2. a=5, b can be 3 or 7 or 2, etc.....------>insuff

E
Director
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Here is my explanation:

1) insuff, dont know what a or b are 8a=5b

2)insuff, this is saying that greatest common factor of a and b is 1
ex. 12 and 7 or any prime number pair ( ex. 2 and 5)

together

5/8= a/b : answers have to be multiples of the numberator and denominator. ex. 10 and 16 or 15 and 24. These answers have common factors. Since 5 and 8 are in its most simplified fraction form, it has to be the answer.

If you can explain it better please let us know. thanks
SVP
Joined: 05 Apr 2005
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joemama142000 wrote:
If a and b are positive integers, what is the value of a + b?
1) a/b = 5/b
2) the greatest comon divisor of a and b is 1

joemama142000 wrote:
Here is my explanation:
1) insuff, dont know what a or b are 8a=5b
2)insuff, this is saying that greatest common factor of a and b is 1
ex. 12 and 7 or any prime number pair ( ex. 2 and 5)
together
5/8= a/b: answers have to be multiples of the numberator and denominator. ex. 10 and 16 or 15 and 24. These answers have common factors. Since 5 and 8 are in its most simplified fraction form, it has to be the answer.
If you can explain it better please let us know. thanks
Director
Joined: 17 Oct 2005
Posts: 932
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Kudos [?]: 105 [0], given: 0

sorry all, my mistake. must have been really tired today. In that case you are correct and the answer is E
Director
Joined: 17 Oct 2005
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Anyway, here is the original question and explanation. I thought it was tricky.

If a and b are positive integers, what is the value of a + b ?
(1) a/b=5/8
(2) The greatest common divisor of a and b is 1.

Here is my explanation:

1) insuff, dont know what a or b are 8a=5b

2)insuff, this is saying that greatest common factor of a and b is 1
ex. 12 and 7 or any prime number pair ( ex. 2 and 5)

together

5/8= a/b : answers have to be multiples of the numberator and denominator. ex. 10 and 16 or 15 and 24. These answers have common factors. Since 5 and 8 are in its most simplified fraction form, it has to be the answer.
Intern
Joined: 29 Jun 2011
Posts: 36
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Kudos [?]: 3 [0], given: 0

Re: [#permalink]  19 Jul 2011, 05:46
joemama142000 wrote:
Anyway, here is the original question and explanation. I thought it was tricky.

If a and b are positive integers, what is the value of a + b ?
(1) a/b=5/8
(2) The greatest common divisor of a and b is 1.

Here is my explanation:

1) insuff, dont know what a or b are 8a=5b

2)insuff, this is saying that greatest common factor of a and b is 1
ex. 12 and 7 or any prime number pair ( ex. 2 and 5)

together

5/8= a/b : answers have to be multiples of the numberator and denominator. ex. 10 and 16 or 15 and 24. These answers have common factors. Since 5 and 8 are in its most simplified fraction form, it has to be the answer.

SORRY! if i'm asking a silly question...

since a/b = 5/8. why can't we just plug in a = 5 and b = 8? Pls explain. thanks!
Senior Manager
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Re: DS integers [#permalink]  19 Jul 2011, 20:22
Damn i thought it was C!
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Re: DS integers [#permalink]  21 Jul 2011, 06:18
1
KUDOS
at miweekend...

consider
a/b=5/8
if u consider some other number 25/40 and simplifying it would also get 5/8 so the value given might not ration not the original value
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Intern
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Re: Re: [#permalink]  22 Jul 2011, 00:33
miweekend wrote:
joemama142000 wrote:
Anyway, here is the original question and explanation. I thought it was tricky.

If a and b are positive integers, what is the value of a + b ?
(1) a/b=5/8
(2) The greatest common divisor of a and b is 1.

Here is my explanation:

1) insuff, dont know what a or b are 8a=5b

2)insuff, this is saying that greatest common factor of a and b is 1
ex. 12 and 7 or any prime number pair ( ex. 2 and 5)

together

5/8= a/b : answers have to be multiples of the numberator and denominator. ex. 10 and 16 or 15 and 24. These answers have common factors. Since 5 and 8 are in its most simplified fraction form, it has to be the answer.

SORRY! if i'm asking a silly question...

since a/b = 5/8. why can't we just plug in a = 5 and b = 8? Pls explain. thanks!

thanks. good explanation indeed. never think of it...
Re: Re:   [#permalink] 22 Jul 2011, 00:33
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