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If the units digit of the three digit positive integer k is

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Director
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If the units digit of the three digit positive integer k is [#permalink]

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20 Jun 2007, 19:27
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If the units digit of the three digit positive integer k is non-zero, what is the tens digit of k?

1. The tens digit of k+9 is 3
2. The tens digit of k+ 4 is 2
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VP
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Re: Units digit of 3 digit positive number - DS [#permalink]

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20 Jun 2007, 19:37
bewakoof wrote:
If the units digit of the three digit positive integer k is non-zero, what is the tens digit of k?

1. The tens digit of k+9 is 3
2. The tens digit of k+ 4 is 2

I got A.

(1) k+9 = A3B
=> k = A3B - 9
B can be 0 to 8. This makes tens digit of k = 2.
SUFFICIENT

(2) k+4 = A2B
=> k = A2B - 4
B can be 0 to 3 and 5 to 9. This makes tens digit of k = 1 or 2
INSUFFICIENT
Director
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21 Jun 2007, 09:21
Slightly different approach...
Let positive integer k be ABC where C does not = 0

A) The ten digit of k+9 = 3 is basically means you add 1 to the ten digit since "C" cannot = 0. Ex) 121+9 = 130...129+9=138. So the ten digit for integer k must be 2.

The trick is to remember k+9 refers to the integer as a whole not the ten digit.

A is sufficient
VP
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21 Jun 2007, 10:31
My two cents:

statement 1

The tens digit of k+9 is 3

the most k+9 can be is x38 and the least x31 - when subtracting 9 the tens digit will always be 2.

x39 cannot be since 9-9 = 0

statement 2

The tens digit of k+ 4 is 2

the most k+4 can be is x29 and the least x21 - when subtracting 4 the tens digit can be 2 or 1.
21 Jun 2007, 10:31
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