The sample proportion is 0.18 (18 divided by 100)
The z-score is 1.64 (Remember that 5% off of both sides is removed)
The margin of error is 0.06
The confidence interval is (0.12,0.24)
The confidence interval means that:
We are 90% confidence that the actually proportion of houses that utilize the bulk trash pick up in a given month is between 0.12 and 0.24 (or 12-24%)
