Question

1. On average, the number of customers who had items to return for refunds or exchanges at a certain retail store's service desk is 756 per week. Find the probability that the service desk will have at least 100 customers with returns or exchanges on a randomly selected day. (Assume the store is open 7 days/week.)

a.	0.208	b.	approximately 1
c.	0.792	d.	approximately 0

2. A recent survey found that 30% of telephone users have switched completely to cell phone use (i.e. they do not have landlines in their homes). A random sample of 10 of these customers is selected.

Would it be considered unusual if there was 1 telephone user in this sample without a landline? What if there were 6 telephone users without landlines?

a.	1 and 6 would both be considered unusual	b.	1 would not be unusual; 6 would be unusual
c.	neither 1 nor 6 would be considered unusual	d.	1 would be unusual; 6 would not be unusual

Answer 1

1) X: Number of customers

Here X follows a Poisson distribution.

= 756

We have to find the probability that the service desk will have at least 100 customers with returns or exchanges on a randomly selected day.

That is P(X 100)

b.	approximately 1

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2)

p = 0.30

n = 10

X follows Binomial distribution.

P(X = 1) = 0.1211

P(X = 6) = 0.0368

( Form Binomial table)

If probability is less than 0.05 we say it is unusual otherwise usual.

Correct answer is

b.	1 would not be unusual; 6 would be unusual