Confidence interval for the proportion of registered users

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Reference no: EM131015193

An e-commerce business wishes to estimate the proportion of its web site users who entered false phone numbers when registering. A sample of 250 users is chosen at random. Of these, 37 are discarded because of database errors. Of the remaining users, 19 had registered with false phone numbers.

(a) Find a 99% confidence interval for the proportion of registered users with false phone numbers and explain what it indicates. Use language that a manager could easily understand.

(b) The manager wants the margin of error to be 2% or less. How large a sample should be taken?

(d) The business is interested in trying to redesign its web site to cut down on the number of registrations with false phone numbers. How large a sample of registrations would be needed if they wanted to test their success using a = 0.1 and wanted to be able to detect a decrease from 10 to 5% with probability 0.8?

Reference no: EM131015193

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