Problem:
Which of the following could not be the unit's digit [one's digit] of the square of a whole number?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
The unit's digit of the square of a whole number is determined by the square of its unit's digit. The possible squares of unit digits are:
Note that , or will never occur as the unit's digit of a square.
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions