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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]

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New post Updated on: 27 Nov 2017, 01:50
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E

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


(1) \(\frac{a}{b} = \frac{5}{8}\)

(2) The greatest common divisor of a and b is 1.


OPEN DISCUSSION OF THIS QUESTION IS HERE: https://gmatclub.com/forum/if-a-and-b-a ... 35199.html

Originally posted by joemama142000 on 30 Nov 2005, 10:51.
Last edited by Bunuel on 27 Nov 2017, 01:50, edited 2 times in total.
Edited the question.
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 30 Nov 2005, 11:28
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
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 30 Nov 2005, 12:15
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
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 30 Nov 2005, 18:21
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


make sure your OE follows your question.

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
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 30 Nov 2005, 18:28
sorry all, my mistake. must have been really tired today. :shock: In that case you are correct and the answer is E
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 30 Nov 2005, 18:34
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.
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 19 Jul 2011, 06:46
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!
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 19 Jul 2011, 21:22
Damn i thought it was C!
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 21 Jul 2011, 07:18
1
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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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 22 Jul 2011, 01:33
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...
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Re: If a and b are positive integers, what is the value of a + b?  [#permalink]

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New post 27 Nov 2017, 01:50
If a and b are positive integers, what is the value of a + b?

(1) \(\frac{a}{b} = \frac{5}{8}\) --> \(a\) and \(b\) could be: (5, 8), (10, 16), (15, 24), ... Not sufficient.

(2) The greatest common divisor of a and b is 1. Clearly insufficient: \(a\) and \(b\) could be any co-prime numbers.

(1)+(2) Since from (2) \(a\) and \(b\) do not share any common factor but 1, then from (1) \(a=5\) and \(b=8\) --> \(a+b=13\). Sufficient.

Answer: C.


OPEN DISCUSSION OF THIS QUESTION IS HERE: https://gmatclub.com/forum/if-a-and-b-a ... 35199.html
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Re: If a and b are positive integers, what is the value of a + b? &nbs [#permalink] 27 Nov 2017, 01:50
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