Let X be the number of weeks before the prices change in a grocery store and p be the probability of updating the prices in a given week. The pricing decision is independent between any two weeks. If the distribution of X is described bywhere x =r, r+ 1,... The average duration of prices in this store is (3) if r =1.

A random variable X represents the number of defective mobile phone is a shipment of four iPhones to a local mobile phone stor(E) Assume that each mobile phone is equally likely to be defective or non-defective, and also assume that each mobile phone is defective or non-defective independently of the other mobile phones. Then the expected number of defective mobile phones is _______.

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