AMC8 1990
AMC8 1990 · Q4
AMC8 1990 · Q4. It mainly tests Perfect squares & cubes.
Which of the following could not be the unit's digit of the square of a whole number?
下列哪一个不可能是某个整数平方的个位数字？
(A)
1
1
(B)
4
4
(C)
5
5
(D)
6
6
(E)
8
8
Answer
Correct choice: (E)
正确答案：（E）
Solution
The unit’s digit of the square of a whole number is determined by the square of the unit’s digit of that whole number. The possible units digits are $0,1,4,5,6,9$. Note that $2,3,7,$ or $8$ will never occur.
整数平方的个位数字由该整数个位数字的平方决定。可能的个位数字是 $0,1,4,5,6,9$。注意 $2,3,7$ 或 $8$ 永远不会出现。
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