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In-action problem set: 5. what is the units digit of y? 1)

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In-action problem set: 5. what is the units digit of y? 1) [#permalink] New post 10 Oct 2011, 21:07
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

82% (01:26) correct 18% (00:29) wrong based on 11 sessions
In-action problem set:

5. 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..

here the OA is C

I think OA is wrong - there is no place where it says y is positive or negative
However, if you take y as a negative value, the ans should be E. What do you think?
[Reveal] Spoiler: OA
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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 10 Oct 2011, 21:20
OA is correct.

karthiksms wrote:
I think OA is wrong - there is no place where it says y is positive or negative
However, if you take y as a negative value, the ans should be E. What do you think?


What difference does it make? Units digit is the last digit and that's what you're interested in.
let y be negative,

1.
last digit of y^2=1
eg. -9^=81
-11^2=121
that means units of digit of y can be 1 or 9.
1 is insufficient

2.
Insufficient as the digit can be 0,2,3,4,5,6,7,8, & 9

1+2
Between 1 & 9, 1 is not possible
Hence
digit is 9
So C

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 10 Oct 2011, 21:26
oh yeah..you're right..thanks
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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 10 Oct 2011, 21:27
I know...
You're welcome

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 10 Oct 2011, 21:43
@blink005.. i see that you got a really high gmat score.. could you tell us what books you used for preparation for both quant and verbal.. thanks
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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 10 Oct 2011, 23:18
karthiksms wrote:
In-action problem set:

5. 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..

here the OA is C

I think OA is wrong - there is no place where it says y is positive or negative
However, if you take y as a negative value, the ans should be E. What do you think?


Please hide the hints in a spoiler.

IMO, the answer should be E, not because y can be -ve or +ve but because y may not be an integer.

e.g.
y=457.56; y^2=209361.1536
y=9; y^2=81

Units digit can be 7 or 9. Not Sufficient.

Ans: "E"

OR, the question should read:

What is the units digit of integer y?

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 11 Oct 2011, 01:05
fluke wrote:
IMO, the answer should be E, not because y can be -ve or +ve but because y may not be an integer.

e.g.
y=457.56; y^2=209361.1536
y=9; y^2=81

Units digit can be 7 or 9. Not Sufficient.

Ans: "E"

OR, the question should read:

What is the units digit of integer y?


Yeah, sorry about that. I overlooked that possibility. I had seen a similar question that stated y was an integer.

There seems to be a similar question-
http://www.manhattangmat.com/forums/uni ... 13490.html

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 11 Oct 2011, 03:11
blink005 wrote:


Yeah, I have seen this. The answer should be "E" for this one too.

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 11 Oct 2011, 08:11
karthiksms wrote:
In-action problem set:

5. 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..

here the OA is C

I think OA is wrong - there is no place where it says y is positive or negative
However, if you take y as a negative value, the ans should be E. What do you think?


Unlike the question in the link, this question doesn't require different solutions for positive/negative numbers.
Statement 1 squares the expression.

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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 11 Oct 2011, 15:17
units digit of y=?

1. Not Sufficient

units digit of y^2 = 1

=>units digit y can be 1 or 9 or 1.21 ..or 1.29...

2. Not Sufficient

units digit of y is not equal to 1.

units digit of y can be 0,2,3,.....9

Together, Not sufficient

y can still be 9 or 1.29 so on..

Answer is E.
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Re: Manhattan Advanced GMAT Quant question [#permalink] New post 12 Oct 2011, 19:55
It should be E. As it is not mentioned that the number is an integer.

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CR notes
http://gmatclub.com/forum/massive-collection-of-verbal-questions-sc-rc-and-cr-106195.html#p832142
http://gmatclub.com/forum/1001-ds-questions-file-106193.html#p832133
http://gmatclub.com/forum/gmat-prep-critical-reasoning-collection-106783.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html?hilit=chineseburned

Re: Manhattan Advanced GMAT Quant question   [#permalink] 12 Oct 2011, 19:55
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In-action problem set: 5. what is the units digit of y? 1)

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