Concerned at the time to react to customer complaints CoCo S.A. has implemented a new set of procedures for its support centre staff. The customer service director has directed that a suitable test is applied to a new sample to assess whether the new target mean time for responding to customer complaints is 28 days (Table 5.9).

(a) Construct a point estimate for the mean time to respond.

(b) What are the model assumptions for part (a)?

(c) Construct a 95% confi dence interval for the mean time.

(d) Is there any evidence to suggest that the mean time to respond to complaints is greater than 28 days?

20 40 32 15 31 28 32 Table 5.9 33 33 50 33 35 22 34 33 20 36 27 19 26 39 29 39 31 29 39 42 39 24 32 38 43 22 30 32 30 37 29 33 21 17 38