A phone company wishes to estimate the mean battery time for their phone. They choose to sample 25 phones and find that the sample average is 325 minutes. Assume that the data is normally distributed. Also assume that s=30 .

Construct a 90% confidence interval.

xtsn

1. What is the appropriate tvalue for the interval?

2. What is the value for the margin of error?

3. What is the value for the lower bound?

4. What is the value for the upper bound?