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

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10 Oct 2011, 22:07

00:00

A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

83% (01:21) correct
17% (00:19) wrong based on 18 sessions

HideShow timer Statistics

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?

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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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?
_________________

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.
_________________

Hit kudos if my post helps you. You may send me a PM if you have any doubts about my solution or GMAT problems in general.

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