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d77
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PostPosted: Wed Dec 13, 2006 7:20 am    Post subject: from gmatprep Reply with quote
If k is a positive integer and the tens digit of k+5 is 4, what is the tens digit of k

1. k>35
2.the unit sigit of k is greater then 5


why is
2
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zipper123
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PostPosted: Wed Dec 13, 2006 8:14 am    Post subject: Re: from gmatprep Reply with quote
d77 wrote:
If k is a positive integer and the tens digit of k+5 is 4, what is the tens digit of k
1. k>35
2.the unit sigit of k is greater then 5
why is
2


1) is not sufficient, because the k can be 37 or 42, which does not provide a unique answer.

Whereas:
2) consider the followings:
If the unit digit is less then 5,
--> k's tens digit is 4
if the unit digit is more than 5,
--> k's tens digit is 3

Therefore condition 2) is sufficient, because it restricts the tens digit to be 3 only.
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d77
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PostPosted: Thu Dec 14, 2006 12:15 pm    Post subject: thanks Reply with quote
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