# What is the z-score of sample X, if n = 169, mu= 42, St. Dev. =39, and E[X] =12?

The z-score is$= - 10$
The z-score for a sample mean is $\frac{\overline{x} - \mu}{\frac{\sigma}{\sqrt{n}}}$
So, here we have $= \frac{12 - 42}{\frac{39}{\sqrt{169}}}$
$= - \frac{30}{3} = - 10$