Is a+b divisible by 7? a and b are both +ve integers. 1) a : GMAT Data Sufficiency (DS)
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# Is a+b divisible by 7? a and b are both +ve integers. 1) a

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Intern
Joined: 16 Jan 2007
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Is a+b divisible by 7? a and b are both +ve integers. 1) a [#permalink]

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04 Aug 2010, 10:29
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35% (medium)

Question Stats:

92% (01:25) correct 8% (00:00) wrong based on 12 sessions

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Is a+b divisible by 7? a and b are both +ve integers.

1) a is not divisible by 7
2) b is not divisible by 7
[Reveal] Spoiler: OA
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GRE 1: 337 Q168 V169
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Kudos [?]: 11 [0], given: 0

Re: Is a+b divisible by 7? [#permalink]

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04 Aug 2010, 10:35
1) let a = 1, then if b = 1 we have a+b not divisible by 7. on the other hand if b =6, a+b is divisible by seven. Not Sufficient
2) Use the same argument as in 1), Not Sufficient
1 & 2) Use the same argument as in 1). Not Sufficient

Hence E
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Re: Is a+b divisible by 7? [#permalink]

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04 Aug 2010, 10:41
Also we can think it this way:

1) Non Multiple (of 7) + Multiple (of 7) = always non multiple (of 7)
where as
2) Non Multiple + Non Multiple = either multiple or non Multiple
3) Multiple + Multiple = always multiple

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Re: Is a+b divisible by 7? [#permalink]

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17 Aug 2010, 14:33

By combining 2 statements

For ex = a+b= 8+15/7 =23/7= not divisible
a+b= 15+6/7=21/7 = divisible
Re: Is a+b divisible by 7?   [#permalink] 17 Aug 2010, 14:33
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