A telecommunication engineer studied the lengths of cellphone calls in a random sample of 70 calls and calculated the mean length to be 146.7 seconds. A cell network reports that the standard deviation among lengths of all calls is 83.4 seconds. Estimate the mean length of all cellphone calls using 96% confidence. Round interval values to 1 digit after the decimal point.

The z critical point to use is z = . Give the value to 3 digits after the decimal.

Summary: Using 96% confidence the mean length among all cellphone calls is between { } seconds and { } seconds.