Explanation
We are to find the z-score for the given data
To do so, we will use the formula:
[tex]z=\frac{x-\mu}{\sigma}[/tex]
where
[tex]\begin{gathered} x=observed\text{ mean=86} \\ \mu=90 \\ \sigma=8 \end{gathered}[/tex]
Therefore,
[tex]\begin{gathered} z_{86}=\frac{86-90}{8}=-\frac{4}{8}=-0.5 \\ \\ z_{86}=-0.5 \end{gathered}[/tex]
The z-score is -0.5
