b. What is the probability that between 50 and 75 (inclusive) had fished?
c. If the 180 men selected for the interview were selected by the marketing department of a sporting-goods company based on information obtained from their mailing lists, what would you conclude about the reliability of their survey results?
Answer:
(a) The probability that fewer than 50 had fished is 0.0002.
(b) The probability that between 50 and 75 (inclusive) had fished is 0.6026.
(c) The survey results are not reliable.
Step-by-step explanation:
Let X = number of men who had fished during the year.
The probability of the random variable X is, p = 0.41.
A random sample of n = 180 men are selected.
The random variable X follows a Binomial distribution with parameters n = 180 and p = 0.41.
A Normal approximation to Binomial is applied when the following conditions are met,
Check:
Thus, the distribution of x can be approximated by a Normal distribution with:
Mean =
Standard deviation =
(a)
Compute the probability that fewer than 50 had fished as follows:
Thus, the probability that fewer than 50 had fished is 0.0002.
(b)
Compute the probability that between 50 and 75 (inclusive) had fished as follows:
Thus, the probability that between 50 and 75 (inclusive) had fished is 0.6026.
(c)
If the sample of 810 men are selected from mailing list then it is highly probable that the sample is not a representative of the true population, i.e. sports men.
Because the people interested in sports are less likely to be interested in fishing.
Thus, it could be concluded that the survey results are not reliable.