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Exercises 91
What is the probability that in the first week:
(a) Four or five units will be sold;
(b) At least 3 units will be sold;
(c) At least 1 unit will be sold?
(3) The managers of a food company are interested in determining
the effect on their sales of a competitor’s television advertisements.
An analysis of sales records for the last 120 weeks gives the
following results:
Level of sales (no. of weeks)
Low Medium High Total
Competitor advertised 32 14 18 64
Competitor did not
advertise
21 12 23 56
Total 53 26 41 120
Assuming that these past data are a reliable guide to the future,
determine the probability that next week:
(a) The competitor will advertise;
(b) Sales will not be high;
(c) Medium or high sales will be achieved;
(d) Either the competitor will advertise or only low sales will
be achieved;
(e) Either the competitor will not advertise or high sales will
be achieved.
(4) (a) With reference to the table in question 3, determine the following
probabilities:
(i) p(next week’s sales will be high)
(ii) p(next week’s sales will be high|the competitor advertises)
(iii) p(next week’s sales will be high|the competitor does not
advertise)
(iv) p(next week’s sales will be low)
(v) p(next week’s sales will be low|the competitor advertises)
(b) Do the events ‘competitor advertises’ and ‘high sales’ appear to
be independent?