Answer: The middle 90% of incomes are between $6621.25 and $12378.75 .
Step-by-step explanation:
The critical z-value for 90% confidence = 1.645
Given: Mean income per household = $9500
standard deviation = $1750
then, middle 90% of incomes are between $(9500-(1.645)(1750)) and (9500+(1.645)(1750))
i.e. middle 90% of incomes are between $6621.25 and $12378.75.
Hence, the middle 90% of incomes are between $6621.25 and $12378.75 .
