Posted by Stuart on Sunday, February 22, 2009 at 4:06pm.
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?
A) 0.84
B) 0.34
C) 0.955
D) 0.75

Statistics  MathGuru, Sunday, February 22, 2009 at 9:48pm
This will be within two standard deviations of the mean. To show this, use zscores.
Formula is this:
z = (x  mean)/sd
Therefore:
z = (75  95)/10 = ?
z = (115  95)/10 = ?
I'll let you finish the calculations. Remember that one zscore is below the mean and one is above the mean.
I hope this will help get you started.
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