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What is the units digit of Y?

(1) The units digit of Y^2 is equal to 6. (2) The units digit of (Y+1)^2 is equal to 5

Its fairly simple problem , but I have a problem with the OA. St1: can be 4 or 6 or - 4 or -6 ... hence in sufficient st2: can be 4 or -6... .. The question doesnt mention the Y is a postive integer..

Q: What is the units digit of Y? st:1 The units digit of Y^2 is equal to 6. St:2 The units digit of (Y+1)^2 is equal to 5

Its fairly simple problem , but I have a problem with the OA. St1: can be 4 or 6 or - 4 or -6 ... hence in sufficient st2: can be 4 or -6... .. The question doesnt mention the Y is a postive integer..

Good catch!!! Stem should have mentioned "positive integer Y", OR the OA should be "E". Please notify them.
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no need to mention positive integer...the question says find "units digit". by definition, units digits can only be non negative integers. so there is no ambiguity.
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It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

Last edited by fivedaysleft on 02 Jul 2011, 10:57, edited 1 time in total.

[quote="fivedaysleft"]no need to mention positive integer...the question says find "units digit". by definition, units digits can only be positve integers. so there is no ambiguity.

quote]

Can anyone confirm this? I'm not aware of any such rule.

I think b is the correct answer. At first even I went for E but a second read of the question says unit digit of Y- so has to be positive. Else the question could be what is Y?

So solution could be as follows: 1) Could be 4 or 6- A and D are out 2) has to be 4- sufficient, B is the answer.

no need to mention positive integer...the question says find "units digit". by definition, units digits can only be positve integers. so there is no ambiguity.

Can anyone confirm this? I'm not aware of any such rule.

fivedaysleft mentioned a partially correct rule. Digit=0,1,2,3,4,5,6,7,8,9 (So a digit is non-negative one-digit integer)

But, note that y is an Integer, any Integer, NOT necessarily a digit.

Unit's digit of "y" is a digit.

y can be -525324324342424246; Here unit's digit of y=6 OR y can be +434252424242424244; Here unit's digit of y=4

Please send a mail to MGMAT and get it clarified.
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y can be -525324324342424246; Here unit's digit of y=6 OR y can be +434252424242424244; Here unit's digit of y=4

Please send a mail to MGMAT and get it clarified.

i dont think the ambiguity is too great. because if a problem is given on the number -525324324342424246 it can always be assigned as (-1)*(525324324342424246) and we can proceed. There might be a difference in definitions of digits and integers at the fundamental level but is it necessary for GMAT? i do not believe so. correct me if i am wrong.
_________________

It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

y can be -525324324342424246; Here unit's digit of y=6 OR y can be +434252424242424244; Here unit's digit of y=4

Please send a mail to MGMAT and get it clarified.

i dont think the ambiguity is too great. because if a problem is given on the number -525324324342424246 it can always be assigned as (-1)*(525324324342424246) and we can proceed. There might be a difference in definitions of digits and integers at the fundamental level but is it necessary for GMAT? i do not believe so. correct me if i am wrong.

If we can find one such ambiguity in OG's OR GmatPrep, then we can think about taking it for granted. It is highly unlikely that GMAT will ever frustrate you with such dilemma. Skip this question and let's wait for MGMAT's response.
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On the real GMAT, any question about units digits will be restricted to *positive* numbers only. So if this were an actual GMAT question, the stem would tell you that Y is positive. I agree that this question is ambiguous as written and needs to be corrected, but if you understand how you'd solve the question if it read "If Y is a positive integer, what it the units digit of Y?" then you've taken away everything you need to take away from the problem.
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