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Advanced Quant Chapter 5, In-Action Problem Set #4 (pg.151)

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jean.hsu.c
 Post subject: Advanced Quant Chapter 5, In-Action Problem Set #4 (pg.151)
 Post Posted: Fri Nov 11, 2011 12:39 pm 
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Students


Posts: 2
Hi,

Question:
4. What is the unit digit of y?

(1) The units digit of y^2 equals 6.
(2) The units digit of (y+1)^2 equals 5.

The answer given for this DS problem is (B). It states that only 5 yields a units digit of 5 when raised to any power. Since the units digit of y+1 is 5, the units digit of y must be 4.


My questions is whether y can be a negative integer with 6 as the units digit, eg. -16, so that (-16+1)^2 also yields a units digit of 5?

Thank you! :-)
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jean.hsu.c
 Post subject: Re: Advanced Quant Chapter 5, In-Action Problem Set #4 (pg.151)
 Post Posted: Thu Nov 17, 2011 2:41 am 
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Students


Posts: 2
Stacey, can you please help to answer my question please? Thank you!!
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jnelson0612
 Post subject: Re: Advanced Quant Chapter 5, In-Action Problem Set #4 (pg.151)
 Post Posted: Sat Dec 10, 2011 9:37 pm 
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ManhattanGMAT Staff


Posts: 1857
Hi Jean,
I have looked at this problem before and think that you are making an excellent point. We should have specified that the variable is a positive integer. Great catch!

_________________
Jamie Nelson
ManhattanGMAT Instructor
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