The amount of Jen's monthly phone bill is normally distributed with a mean of $55 and a standard deviation of $12. Calculate the z score for each scenario.

Question

What percentage of her phone bills are above 79?
What percentage of her phone bills are between $31 and $79.
What would be the z score and monthly bill of somone in the top 5% of monthly phone bills?

Answer 1

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability for each Z score. For last question, use the table to find .05 and insert its Z score in the equation above.