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If r is divisible by 10 and s is divisible by 9, rs must hav

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GMAT Club Legend
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Joined: 07 Jun 2014
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GRE 1: Q167 V156
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If r is divisible by 10 and s is divisible by 9, rs must hav [#permalink] New post 12 Aug 2018, 15:41
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Question Stats:

53% (01:17) correct 46% (00:10) wrong based on 13 sessions
If r is divisible by 10 and s is divisible by 9, rs must have at least how many factors?

(A) Two
(B) Four
(C) Twelve
(D) Fourteen
(E) Sixteen
[Reveal] Spoiler: OA

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GMAT Club Legend
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Re: If r is divisible by 10 and s is divisible by 9, rs must hav [#permalink] New post 15 Aug 2018, 08:19
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Explanation

This problem is most easily solved with an example. If r = 10 and s = 9, then rs = 90. The factors of 90 are 1 & 90, 2 & 45, 3 & 30, 5 & 18, 6 & 15, and 9 & 10. Count to get a minimum of 12 factors.
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Re: If r is divisible by 10 and s is divisible by 9, rs must hav [#permalink] New post 31 Aug 2018, 08:56
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RS is 90.. so in order to count the number of factors of 90 we need to see prime factorization of 90

we get 3*3*2*5

now we have 3 -- twice and 2 and 5 once

we add 1 to each of their power and multiple the power- 3*2*2= 12 hence the answer is C.
Re: If r is divisible by 10 and s is divisible by 9, rs must hav   [#permalink] 31 Aug 2018, 08:56
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If r is divisible by 10 and s is divisible by 9, rs must hav

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