5. Given that the average of 8 numbers is 8, if one of the numbers is changed to 8, the average of these 8 numbers becomes 7, then the original number that was changed is $\qquad$ .
【Analysis】If one of the numbers is changed to 8, the average changes from 8 to 7, indicating that the total sum has decreased. According to the "method of redistribution," the average has decreased by $8-7=1$, and the total has decreased by $8 \times 1=8$. The number that was changed is $8+8=16$; solve accordingly.

【Solution】Solution: $(8-7) \times 8+8$
$$
\begin{array}{l}
=8+8 \\
=16
\end{array}
$$

Answer: The number that was changed was originally 16.
Therefore, the answer is: 16.