What is and what is not?
If is a positive integer such that the units (ones) digit of is and the units digit of is not , what is the units digit of ?
The answer is 2.
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1 solution
* (i'm not sure because i have 2 solution ) *
n^{2} + 4n = n \time ( n+3 + 1 ) = somenumber have unit is 7
n and ( n +3 +1 ) have unit 3 or 9 ( because 3 \time 9 = 27 )
Hence, we have 2 solution:
If n have unit is 3 --> (n + 3) have unit is 8.
If n have unit is 9 --> (n + 3) have unit is 2 (the correct answer for this question ).