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units digit of (n + 2)^2

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by sanju09 » Fri Jan 28, 2011 3:56 am
n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9



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by Anurag@Gurome » Fri Jan 28, 2011 4:08 am
sanju09 wrote:n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9
As the unit's digit of n² is 5, unit's digit of n is also 5.
Hence, unit's digit of (n + 2) is 7.

Therefore, unit's digit of (n + 2)² will be unit's digit of 7*7 = 49, i.e. 9.

The correct answer is E.
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by sanju09 » Fri Jan 28, 2011 4:36 am
Anurag@Gurome wrote:
sanju09 wrote:n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9
As the unit's digit of n² is 5, unit's digit of n is also 5.
Hence, unit's digit of (n + 2) is 7.

Therefore, unit's digit of (n + 2)² will be unit's digit of 7*7 = 49, i.e. 9.

The correct answer is E.
right answer by chance...

if units digit of integer n is 5, then n could be either positive or negative, and units digit of integer n + 2 is 7 when n is positive, but it's 3 if n is negative, but in both cases units digit of integer n^2 is always 9.
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by lenagmat » Tue Oct 25, 2011 11:25 am
Is it ALWAYS:
As the unit's digit of n² is 5, unit's digit of n is also 5.

I mean if the unit's digit of n^2 is 9, unit's digit of n is also 9??

Anurag@Gurome wrote:
sanju09 wrote:
As the unit's digit of n² is 5, unit's digit of n is also 5.
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