DS: t divided by 7 : DS Archive - Page 2
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# DS: t divided by 7

Author Message
Manager
Joined: 14 Jun 2007
Posts: 170
Location: Vienna, Austria
Followers: 1

Kudos [?]: 7 [0], given: 0

Re: DS: t divided by 7 [#permalink]

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08 Sep 2008, 00:47
friends, whats the OA ??
Current Student
Joined: 04 Jan 2005
Posts: 283
Location: Milan
Schools: Wharton, LBS, UChicago, Kellogg MMM (Donald Jacobs Scholarship), Stanford, HBS
Followers: 7

Kudos [?]: 140 [0], given: 3

Re: DS: t divided by 7 [#permalink]

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08 Sep 2008, 04:18
judokan,

as per the second question, I tried picking numbers:

65 (sum of digits 11), remainder 2
92 (sum of digits 11), remainder 2
499 (sum of digits 22), remainder 4
6999 (sum of digits 33), remainder 6

how could it be A? Or do I miss something in the question?
Senior Manager
Joined: 19 Mar 2008
Posts: 354
Followers: 1

Kudos [?]: 54 [0], given: 0

Re: DS: t divided by 7 [#permalink]

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08 Sep 2008, 05:28
judokan,

as per the second question, I tried picking numbers:

65 (sum of digits 11), remainder 2
92 (sum of digits 11), remainder 2
499 (sum of digits 22), remainder 4
6999 (sum of digits 33), remainder 6

how could it be A? Or do I miss something in the question?

Tks Para for pointing that out.

I just made up the question from memory.

I think n should be the digit should be divisible by 11, instead of multiciple of 11.

Tks
SVP
Joined: 29 Aug 2007
Posts: 2492
Followers: 67

Kudos [?]: 734 [0], given: 19

Re: DS: t divided by 7 [#permalink]

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08 Sep 2008, 08:19
judokan wrote:
(1) t = 7k + 6 (where k is integer)
t^2 + 5t +6
= 49k^2 + 14k + 36 + 35k + 30 + 6
= 49k^2 + 14k + 72
(the first two terms are multiple of 7)
so the reminder is equal to the remainder when 72 divided by 7, i.e. 2
(1) is sufficent

(2) t^2 = 7i +1 (where k is integer)
t^2 + 5t +6
= 7i + 1 + 5t + 6
= 7i + 7 + 5t
(the first two terms are multiple of 7)
so the reminder is equal to the remainder when 5t divided by 7

Now we try to find out the remainder when 5t divided by 7:
when i = 0, t^2 = 1, t = 1, remainder of t when divided by 7 = 1
when i = 5, t^2 = 36, t = 6, remainder of t when divided by 7 = 6
so, it give different results.
(2) alone is not suff.

Ans is A

1: agree with above
2: t could be1 or 6 or 8 and so on. r is different for t = 1, t = 6 and t = 8.
so nsf.

So A.
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Re: DS: t divided by 7   [#permalink] 08 Sep 2008, 08:19

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