Credit card sales The National Association of Retailers reports that 62% of all purchases
are now made by credit card; you think this is true at your store as well. On a typical day
you make 20 sales.
a. Explain why your sales can be considered Bernoulli trials.
b. What is the probability that your fourth customer is the first one who uses a credit card?
c. Let X represent the number of customers who use a credit card on a typical day. What is
the probability model for X? Specify the model (name and parameters), and tell the mean
and standard deviation.
d. What is the probability that on a typical day at least half of your customers use a credit
card?

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The Answer of Credit card sales The National Association of Retailers reports that 62% of all purchases
are now made by credit card; you think this is true at your store as well. On a typical day
you make 20 sales.
a. Explain why your sales can be considered Bernoulli trials.
b. What is the probability that your fourth customer is the first one who uses a credit card?
c. Let X represent the number of customers who use a credit card on a typical day. What is
the probability model for X? Specify the model (name and parameters), and tell the mean
and standard deviation.
d. What is the probability that on a typical day at least half of your customers use a credit
card?

Credit Card Sales the National Association of Retailers Reports That