Unit digit of $123456^{2}$ is

Unit digit of $123456^{2}$ is
  1. $6$
  2. $4$
  3. $2$
  4. $0$

Solution

Unit digit depends only on the unit digit of $123456$, which is $6$. $6^{2} = 36$, so unit digit is $6$.

Asked in: IMO

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