A perfect square never has unit digit

A perfect square never has unit digit
  1. $0$
  2. $1$
  3. $4$
  4. $8$

Solution

Unit digits of perfect squares can only be $0, 1, 4, 5, 6, 9$. So $2, 3, 7, 8$ never appear as the unit digit.

Asked in: IMO

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