A company receives telephone calls at random at a mean rate of 2.5 per hour.
Find the probability that the company receives
at least 4 telephone calls in the next hour,
exactly 3 telephone calls in the next 15 minutes.
Find, to the nearest minute, the maximum length of time the telephone can be left unattended so that the probability of missing a telephone call is less than 0.2
The company puts an advert in the local newspaper. The number of telephone calls received in a randomly selected 2 hour period after the paper is published is 10
Test at the 5\% level of significance whether or not the mean rate of telephone calls has increased. State your hypotheses clearly.