(1) draw a graph with 45,000 at the 0
(2) put 81,000 and 9,000 on the graph with corresponding z scores
(3) integrate
Household income does not tend to follow a normal distribution in a particular state, yet average income is approximately $45,000/year in this state, with a standard deviation of about $9000. At least what percentage of household incomes in this state is likely to be between $9,000 to $81,000/year
Not sure what formula to use?
My husband tried to help me and he came up with 99%. Anyone?
In order to find the area under the normal probability density curve, you need the lower and upper bounds traditionally called z-scores.
A z-score is obtained by subtracting the given x value minus the mean and then dividing by the standard deviation.
Once you have obtained you lower and upper bounds, you can consult the the t-distribution for samples over 120 but your z-scores are so far out they won't be in the table; therefore, you need to integrate.