Real Numbers (OG13, p.281, Q.75)

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Real Numbers (OG13, p.281, Q.75)

by schao » Sun Jan 13, 2013 7:27 am
Is the positive two-digit integer N less than 40?
1) The units digit of N is 6 more than the tens digit.
2) N is 4 less than 4 times the units digit.

Can someone please help me with how to approach this question?
I have looked at the OG explanation but I don't quite get it.

Thanks!
Sherry

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by GMATGuruNY » Sun Jan 13, 2013 9:25 am
schao wrote:Is the positive two-digit integer N less than 40?
1) The units digit of N is 6 more than the tens digit.
2) N is 4 less than 4 times the units digit.

Can someone please help me with how to approach this question?
I have looked at the OG explanation but I don't quite get it.

Thanks!
Sherry
Statement 1: The units digit of N is 6 more than the tens digit.
Since the units digit is 6 more than the tens digit, and the GREATEST possible value of the units digit is 9, the GREATEST possible value of the tens digit = 9-6 = 3.
Thus, the GREATEST possible value of N = 39, which is less than 40.
SUFFICIENT.

Statement 2: N is 4 less than 4 times the units digit.
Since N is 4 less than 4 times the units digit, and the GREATEST possible value of the units digit is 9, the GREATEST possible value of N = (4*9) - 4 = 32, which is less than 40.
SUFFICIENT.

The correct answer is D.
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