To calculate the z-score for a given population mean, μ, and a given standard deviation, σ, we use the following equation:
[tex]z=\frac{x-\mu}{\sigma}[/tex]We know x = 138, μ = 150 and σ = 30, so we can just input that:
[tex]z=\frac{138-150}{30}=\frac{-12}{30}=-0.4[/tex]So the z-sorce of 138 in this test is -0.4.
