Assuming a normal distribution, if 90 percent of the filings cost less than $172

Question

Assuming a normal distribution, if 90 percent of the filings cost less than $172.00, what is the standard deviation? Hint: Use Excel or Appendix C-2 to find the z-score. (Round your answer to 2 decimal places.)

Assuming a normal distribution, if 90 percent of the filings cost less than $172.00, what is the standard deviation? Hint: Use Excel or Appendix C-2 to find the z-score. (Round your answer to 2 decimal places.)

Explanation / Answer

Solution:-

For 90 percent confidence interval, z-score= 1.282

The basic z score formula for a sample is:
z = (x – ) /

The average cost of an IRS Form 1040 tax filing at Thetis Tax Service , =$150.00

Null hypothesis, H0 : x = 172.00

Alternative hypothesis , H1: x <172.00

z = (x – ) /

1.282= (172-150)/

=17.16

The standard deviation is 17.16

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