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If a and b are integers, is 5 a factor of ab?

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Director
Joined: 07 Jun 2004
Posts: 555
Location: PA
If a and b are integers, is 5 a factor of ab?  [#permalink]

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25 Sep 2010, 09:21
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Difficulty:

45% (medium)

Question Stats:

61% (00:48) correct 39% (00:56) wrong based on 71 sessions

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If a and b are integers, is 5 a factor of ab?

(1) a is divisible by 10

(2) b is a factor of 5
Math Expert
Joined: 02 Sep 2009
Posts: 58445
If a and b are integers, is 5 a factor of ab?  [#permalink]

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25 Sep 2010, 09:37
If a and b are integers, is 5 a factor of ab?

(1) a is divisible by 10 --> 5 is a factor of a --> 5 is a factor ab (as a and b are integers). Sufficient.

(2) b is a factor of 5 --> if b = 1 and a is not a multiple of 5 then the answer would be NO but if b = 5 then the answer would be YES. Not sufficient.

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Joined: 06 Aug 2010
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Re: If a and b are integers, is 5 a factor of ab?  [#permalink]

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28 Sep 2010, 08:25
rxs0005 wrote:
If a and b are integers , is 5 a factor of a * b

a is divisible by 10

b is a factor of 5

(1) Since 10 is a multiple of 5, a is divisible by 5. Then ab must be divisible by 5 as well. Sufficient.
(2) b must either be 1 or 5. If b is 5, then ab is divisible by 5, but if b is 1, then ab = a, and we don't know if a is divisible by 5. Insufficient.

A
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Re: If a and b are integers, is 5 a factor of ab?  [#permalink]

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17 Aug 2017, 07:48
if not careful ...silly mistake will happen .

Be careful with factors, multiple concepts !!!
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Re: If a and b are integers, is 5 a factor of ab?   [#permalink] 17 Aug 2017, 07:48
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