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Re: What is the Units digit of Y [#permalink]
11 Nov 2012, 02:07

1

This post received KUDOS

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. _________________

Re: What is the Units digit of Y [#permalink]
11 Nov 2012, 02:24

1

This post received KUDOS

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.

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

gmatclubot

Re: What is the Units digit of Y
[#permalink]
27 Nov 2012, 06:52

Harvard asks you to write a post interview reflection (PIR) within 24 hours of your interview. Many have said that there is little you can do in this...