a+b

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

by kanha81 » Tue May 19, 2009 9:36 am

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

1) a/b = 5/8
2) greatest common divisor of a and b is 1

Please explain

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Source: Beat The GMAT — Data Sufficiency | Tue May 19, 2009 9:36 am

iamcste: Legendary Member; Posts: 940; Joined: Tue Aug 26, 2008 3:22 amFollowed by: 1 member; Thanked: 55 times

Re: a+b

by iamcste » Tue May 19, 2009 9:48 am

kanha81 wrote:If a and b are positive integers, what is the value of a + b ?

1) a/b = 5/8
2) greatest common divisor of a and b is 1

Please explain

IMO C

Individually we dont know a and b hence a+ b is not known

when we know HCF is 1 and ratio of a/b= 5/8, this means a=5 and b=8, a+b=13

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DeepakR: Master | Next Rank: 500 Posts; Posts: 158; Joined: Tue Sep 30, 2008 8:47 amFollowed by: 1 member; Thanked: 23 times; GMAT Score:660

by DeepakR » Tue May 19, 2009 9:52 am

I think it is C.)

1. a/b=5/8 so a can be 5,10 etc and b can be 8, 16 etc..insufficient

2. GCD of a and b = 1 but a can be 2 or 3 and be can be 3 or 4 insufficient.

Combining we can say that a=5 and b=8 is the only value that satisfies.

- Deepak

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