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# What is the units digit of positive integer x?

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Intern
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What is the units digit of positive integer x?  [#permalink]

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26 Mar 2019, 01:03
2
00:00

Difficulty:

55% (hard)

Question Stats:

60% (01:20) correct 40% (01:44) wrong based on 55 sessions

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What is the units digit of positive integer x?

(1) Units digit of x^2 = 4

(2) Units digit of (x+1)^2 = 1
Manager
Joined: 05 Oct 2017
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Schools: ISB '21, IIMA , IIMB
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WE: Analyst (Energy and Utilities)
Re: What is the units digit of positive integer x?  [#permalink]

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26 Mar 2019, 11:18
Krish0123 wrote:
What is the units digit of positive integer x?

(1) Units digit of x^2 = 4

(2) Units digit of (x+1)^2 = 1

From 1)

Unit digit of x are 2 and 8 then Units digit of x^2 = 4. Two values of unit digit of x is possible 2 and 8.Hence insufficient.

From 2)

If Unit digit x are 0 and 8 then Unit digit of (x+1)^2 will be 9^2 and 1^2. i.e ending in 1. So again here two values for unit digit of x are possible 0 and 8. Hence insufficient.

1+2
From 1) unit digits 2 and 8
From 2) unit digits 0 and 8
So from both the statement it can be concluded unit digit of x=8.

Director
Joined: 23 Feb 2015
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GMAT 1: 720 Q49 V40
Re: What is the units digit of positive integer x?  [#permalink]

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01 Apr 2019, 09:18
Krish0123 wrote:
What is the units digit of positive integer x?

(1) Units digit of $$x^2 = 4$$

(2) Units digit of $$(x+1)^2 = 1$$

1) Units digit of $$x^2 = 4$$:
If x=2,8,18, then we get 4,64,324 respectively. So Insufficient.

2) Units digit of $$(x+1)^2 = 1$$:
If x=0,8,18 we get 1,81,361 respectively. So, insufficient.
Combining (1+2):
From 1 and 2, the most common are 8,18 where the unit(s) digit of positive integer x is 8. So, sufficient.
So, the correct choice is .
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Re: What is the units digit of positive integer x?  [#permalink]

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07 Apr 2019, 13:45
Statement 1 :

Unit digit of x can be 2 or 8 .Hence insufficient.

Statement 2 :

x can be 0 or 8 .Hence insufficient.

1+2
From 1) unit digits 2 and 8
From 2) unit digits 0 and 8
So from both the statement it can be concluded unit digit of x=8.

Re: What is the units digit of positive integer x?   [#permalink] 07 Apr 2019, 13:45
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