The Number of Telephone Calls Coming into a Business' Switchboard

Short Answer

The number of telephone calls coming into a business' switchboard averages 4 calls per minute. Let x be the number of calls received.
Find P(x = 0).
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What is the probability there will be at least one call in a given one-minute period?
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What is the probability at least one call will be received in a given two-minute period?
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