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GMATPrep integer q

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GMATPrep integer q

by aimhigh715 » Sun Dec 09, 2007 12:28 pm
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 digit of k is greater than 5

________

1) tells you that k could be 36 and more. Given 36 + 5 = 41 which does give you 4 on the tenth digit, doesn't that mean it's sufficient?? SUFF


2) Having unit digit higher than 5 and k + 5 giving you 4 in the tenth digit must mean k is within 36-39 range. SUFF

I picked D. Why is it wrong? Thanks in advance!
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by Tud » Sun Dec 09, 2007 2:55 pm
1) insufficient, K could be anywhere between 35 and 44, so the tens could be 3 or 4. Statement one doesn't tell us anything more than what we know from K+5 being in the forties. Remember, it's looking for the tens digit of k, not K+5.

2) Sufficient. You are correct on this one. If the unit digit is greater than 5 then that rules out all the numbers from 45 and above, because they would end up with a tens digit of 5 after k+5. Also, it rules out all the number from 40-44 because their unit digits are less than 5. This limits the value of K from 36-39, so the tens has to be 3.
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