The Internal Revenue Service (IRS) determines which income tax returns to audit by looking at, among other things, whether there are any unusual deductions claimed on the return. Last year, charitable deductions for a family of four earning between $50,000 and $55,000 averaged $1025, with a standard deviation of $150. The IRS wishes to know whether the standard deviation this year is still around $150. To determine this, 28 income tax returns for families of four earning between $50,000 and $55,000 were randomly selected from this year's tax filings. The charitable deductions claimed on the returns are summarized in the following histogram:
Frequency
15-
10-
12
5-
6
6
4
0
900
1000
1100
1200
1300
Charitable deduction (in dollars)
Based on this histogram, estimate the standard deviation of the sample of 28 deduction amounts.
Carry your intermediate computations to at least four decimal places, and round your answer to at least one decimal place.
(If necessary, consult a list of formulas.)