Last Digit - Insight

When you divide a number by $10$, the remainder is the last digit. For example, $12345 \div 10 = 1234$ with remainder $5$.

So the last digit of $n$ is $n \bmod 10$. This works for any positive integer.

Similarly, $\lfloor n / 10 \rfloor$ removes the last digit. If $n = 12345$, then $\lfloor n / 10 \rfloor = 1234$.