题目信息
If n = p2 and p is a prime number greater than 5, what is the units digit of n2 ?
A:1
B:3
C:4
D:7
E:9
参考答案及共享解析
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正确答案：
A:1
Arithmetic Properties of integers
First, all prime numbers greater than 5 are odd numbers with units digit 1, 3, 7, or 9. Note that no prime number greater than 5 has units digit 5. The following table summarizes the results for the possible cases.
The correct answer is A.
First, all prime numbers greater than 5 are odd numbers with units digit 1, 3, 7, or 9. Note that no prime number greater than 5 has units digit 5. The following table summarizes the results for the possible cases.
| Units digit of p | Units digit of p2 = n | Units digit of p4 = n2 |
| 1 | 1 | 1 |
| 3 | 9 | 1 |
| 7 | 9 | 1 |
| 9 | 1 | 1 |
The correct answer is A.
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