The Springfield Emergency Medical Service keeps records of emergency telephone calls. A study of 150 five-minute time intervals resulted in the distribution of number of calls as follows. For example, during 18 of the 5-minute intervals, no calls occurred. Use the chi-square goodness-of-fit test and a = .01 to determine whether this distribution is Poisson.

Number of Calls

(per 5-minute interval) Frequency

0 ...............18

1 ...............28

2 ...............47

3 ...............21

4 ...............16

5 ...............11

6 or more .......... 9