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# If the two-digit integers M and N are positive and have the

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VP
Joined: 09 Jul 2007
Posts: 1098

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Location: London
If the two-digit integers M and N are positive and have the [#permalink]

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02 Oct 2007, 12:43
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If the two-digit integers M and N are positive and
have the same digits, but in reverse order, which of
the following CANNOT be the sum of M and N ?
(A) 181
(B) 165
(C) 121
(D) 99
(E) 44

Kudos [?]: 141 [0], given: 0

Current Student
Joined: 31 Aug 2007
Posts: 368

Kudos [?]: 163 [0], given: 1

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02 Oct 2007, 12:46
product cannot be a multiple of 11, so 181...

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VP
Joined: 08 Jun 2005
Posts: 1144

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02 Oct 2007, 12:49
M = x*10 + y
N = 10*y + x

so:

x*10 + y + 10*y + x = 11*y + 11*x = 11*(y+x)

so the answer cannot be a multiply of 11

Kudos [?]: 246 [0], given: 0

Director
Joined: 09 Aug 2006
Posts: 754

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02 Oct 2007, 13:09
Ravshonbek wrote:
If the two-digit integers M and N are positive and
have the same digits, but in reverse order, which of
the following CANNOT be the sum of M and N ?
(A) 181
(B) 165
(C) 121
(D) 99
(E) 44

A.

1st integer = MN = 10M + N
2nd integer = NM = 10N + M

Sum = 10M + N + 10N + M = 11M + 11N = 11 (M+N)
Therefore, sum of M+N is a multiple of 11. Anything that isn't a multiple of 11 in the answer choices is out answer. 181 is it.

Kudos [?]: 255 [0], given: 0

Re: back to basics   [#permalink] 02 Oct 2007, 13:09
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