In 2020, the average charge of tax preparation was $95. Assuming a normal distribution and a standard deviation of $10, use the approximate areas beneath the normal curve, as discussed in this section, to answer the following questions.
What proportion of tax preparation fees were between $75 and $115?
This will be within two standard deviations of the mean. To show this, use z-scores.
Formula is this:
z = (x - mean)/sd
z = (75 - 95)/10 = ?
z = (115 - 95)/10 = ?
I'll let you finish the calculations. Remember that one z-score is below the mean and one is above the mean.
I hope this will help get you started.posted by MathGuru