What is the Units digit of Y : GMAT Data Sufficiency (DS)
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# What is the Units digit of Y

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Senior Manager
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What is the Units digit of Y [#permalink]

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11 Nov 2012, 00:42
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Question Stats:

74% (01:35) correct 26% (00:47) wrong based on 57 sessions

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What is the Units digit of Y?

(1) The units digit of y^2 = 1

(2) The units digit of y does not equal 1.

Source: MGMAT Advanced Quant.
[Reveal] Spoiler: OA

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Senior Manager
Joined: 03 Sep 2012
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Location: United States
Concentration: Healthcare, Strategy
GMAT 1: 730 Q48 V42
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Kudos [?]: 175 [0], given: 31

Re: What is the Units digit of Y [#permalink]

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11 Nov 2012, 00:47
Having a bit of an issue with this DS problem.

The question stem DOES NOT tell us that Y is either a Single Digit No. or a two digit number..

(1) The unit digit of y^2 = 1 ... Y therefore could be any one of the following numbers:

1, 9, 11 (11 x 11 = 121 , unit digit of 121 is one), 19, 21, 29....

So statement One is not suff.

(2) The units digit of Y does not equal 1.

Not suff.

Taking 1 and 2 together we can remove the following numbers from the list :

1,11,21,31 etc ..

This still leaves, 9 , 19, 29, 39..The squares of all result in a NUMBER whose UNIT digit is 1 ..

Why is the official answer ASSUMING that Y has only one digit when it is not mentioned?
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Re: What is the Units digit of Y [#permalink]

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11 Nov 2012, 02:07
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vomhorizon wrote:
Having a bit of an issue with this DS problem.

The question stem DOES NOT tell us that Y is either a Single Digit No. or a two digit number..

(1) The unit digit of y^2 = 1 ... Y therefore could be any one of the following numbers:

1, 9, 11 (11 x 11 = 121 , unit digit of 121 is one), 19, 21, 29....

So statement One is not suff.

(2) The units digit of Y does not equal 1.

Not suff.

Taking 1 and 2 together we can remove the following numbers from the list :

1,11,21,31 etc ..

This still leaves, 9 , 19, 29, 39..The squares of all result in a NUMBER whose UNIT digit is 1 ..

Why is the official answer ASSUMING that Y has only one digit when it is not mentioned?

Read the question carefully. They are asking the units digit of Y. Not the number Y itself. 9, 19, 29, 39,..... are all values of Y; agreed. But the units digit will always remain 9. Thus, answer is C.
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Re: What is the Units digit of Y [#permalink]

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11 Nov 2012, 02:24
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Agree with TH03 response, we need to concentrate on the unit digit as the questions ask for its value in the question.

(1) The unit digit of y^2 = 1 .

This comes down to either to 1 or 9 as unit digit (the number could be 1,11,21 or 9,19,29 etc)
Not sufficient
(2) The units digit of Y does not equal 1.
This could be anything from 0, 9 except 1
Not suff.

Combining both of them we reach the answer is (C) as 9 is the last digit.
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Re: What is the Units digit of Y [#permalink]

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11 Nov 2012, 02:27
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avi2crackgmat wrote:
Agree with TH03 response, we need to concentrate on the unit digit as the questions ask for its value in the question.

Thanks! I would love kudos too!
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Re: What is the Units digit of Y [#permalink]

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11 Nov 2012, 03:06
Thx for the reply..I;ma go smack my head against a wall now ...
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Re: What is the Units digit of Y [#permalink]

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27 Nov 2012, 06:52
But the question doesn't specify that y has to be an integer. For example y could be 21^1/2, in which case it's unit digit would be 4, or y could be 9, so I think E should be correct.
Re: What is the Units digit of Y   [#permalink] 27 Nov 2012, 06:52
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