Suppose the number of dollars spent per week on groceries is normally distributed. If the population standard deviation is7

dollars, what minimum sample size is needed to be90%

confident that the sample mean is within3

dollars of the true population mean?

z

0.10

1.282

z

0.05

1.645

z

0.025

1.960

z

0.01

2.326

z

0.005

2.576

Use the table above for thez

-score, and be sure to round up to the nextinteger.