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If y is a positive integer, what is the units digit of y?

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If y is a positive integer, what is the units digit of y?  [#permalink]

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New post 29 Sep 2017, 19:53
1
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A
B
C
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If y is a positive integer, 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


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Re: If y is a positive integer, what is the units digit of y?  [#permalink]

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New post 29 Sep 2017, 20:01
C

St1 says y can be an integer with unit digit 9 or 1

St2 clearly not sufficient.

Combining we can conclude the unit digit is 9. Hence C


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Re: If y is a positive integer, what is the units digit of y?  [#permalink]

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New post 07 Feb 2019, 23:17
csaluja wrote:
If y is a positive integer, 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: Manhattan


Keyword : y is a positive integer

UD of y

from 1, we can get 2 values 9 and 1

from 2, we can get 8 values

Combination will give us an unique value, i.e. 1

C
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Re: If y is a positive integer, what is the units digit of y?  [#permalink]

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New post 26 Aug 2019, 23:25
Hi,

This is a pretty simple question if you know about cyclicity. If not, read about cyclicity of numbers before seeing the solution below.

We know y is a positive integer.
Question asks for the units digit of y.

We need to have value of y or some relationship to know about the units digit of y.

Statement 1: Units digit of \(y^2\) = 1
This is possible only if units digit of y = 1 or 9
Two possible values

Insufficient

Statement 2: Units digit of \(y\neq{1}\)
=> y = 2, 3, 4, 5, 6, 7, 8, 9, 0

Insufficient

Combine the information from both the statements. We get only 1 value i.e. 1.

Sufficient

So, the answer is C.


Please give kudos if you liked the solution. :)


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Re: If y is a positive integer, what is the units digit of y?   [#permalink] 26 Aug 2019, 23:25
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