An emergency call service centre keeps records of emergency telephone calls. A study of 150 five-minute time intervals resulted in the following distribution of number of calls. For example, during 18 of the five-minute intervals, no calls were received. Use the chi-square goodness-of-fit test and α =0.01 to determine whether this distribution is Poisson. Explain your test result.

Number of calls
(per 5-minute interval) ................................ Frequency
0 ............................................................................ 18
1 ............................................................................ 28
2 ............................................................................ 47
3 ............................................................................ 21
4 ............................................................................ 16
5 ............................................................................ 11
6 or more ............................................................... 9