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What is the units digit of Y? 29 Jun 2011, 01:25
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

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25% (medium)

Question Stats:

69% (01:08) correct 31% (01:10) wrong based on 160 sessions

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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..

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B
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fluke
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What is the units digit of Y? 29 Jun 2011, 03:56
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sudhir18n
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..
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Good catch!!! Stem should have mentioned "positive integer Y", OR the OA should be "E". Please notify them.
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What is the units digit of Y? Updated on: 02 Jul 2011, 11:57
Originally posted by fivedaysleft on 30 Jun 2011, 01:24.
Last edited by fivedaysleft on 02 Jul 2011, 11:57, edited 1 time in total.
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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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What is the units digit of Y? 30 Jun 2011, 02:58
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[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.
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What is the units digit of Y? 30 Jun 2011, 03:15
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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.

B
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What is the units digit of Y? 30 Jun 2011, 03:18
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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.

Can anyone confirm this? I'm not aware of any such rule.
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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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What is the units digit of Y? 02 Jul 2011, 12:00
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fluke

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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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. :?
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What is the units digit of Y? 02 Jul 2011, 12:25
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fivedaysleft
fluke

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. :?
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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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What is the units digit of Y? 03 Jul 2011, 04:53
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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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What is the units digit of Y? 14 Oct 2018, 07:32
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Hi Bunuel, requesting a clarification on this one.

Why can't we take the case of NEGATIVE Numbers in this one?
Do we always assume that for any question involving a DIGIT on the GMAT, the number is a positive number?
Either the Question is drafted incorrectly or the OA is incorrect.

Here, using B, one has a definitive ans as 4 if its a positive number.

What if its (-8372893729836 + 1)^2. The units digit is still 5.
So if we consider both positive and negative numbers, we have 821829714 or -434236, y has units digit 4 or 6.

Questions should set a condition: Positive or Negative Integer y.

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