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Bunuel
Suppose n is an integer such that \(2 < n^2 <100\). If the units digit of \(n^2\) is 6 and the units digit of \((n —1)^2\) is 5, what is the units digit of \((n +1)^2\)?

(A) 2
(B) 4
(C) 6
(D) 8
(E) 9

The units digit of \((n —1)^2\) is 5. A power has a unit digit of 5 only when the base also has a unit digit of 5. Then \(n - 1\) must be equal to 5 and \((n + 1)^2 = 7^2 = 49\).

Ans: E
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Bunuel
Suppose n is an integer such that \(2 < n^2 <100\). If the units digit of \(n^2\) is 6 and the units digit of \((n —1)^2\) is 5, what is the units digit of \((n +1)^2\)?

(A) 2
(B) 4
(C) 6
(D) 8
(E) 9

The units digit of \((n —1)^2\) is 5. A power has a unit digit of 5 only when the base also has a unit digit of 5. Then \(n - 1\) must be equal to 5 and \((n + 1)^2 = 7^2 = 49\).

Ans: E
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Given the constraint that 2<n^2<100, n has to be a single digit number.Since the question asks for the units digit of (n+1)^2, I did not bother with the possibility of negative values for n.For the units digit of n^2 to be 6, n can be either 4 or 6.With the next piece of information that the units digit of (n-1)^2 is 5, we know that n-1=5 which means n=6 which would help us get the units digit of (n+1)^2 which would be 7*7=49.

Hope this helps.
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