11.4.1. Calculating Probability

In a store selling computer sets, given that the probability of selling 31 sets at least daily is 0.79, and the probability of selling less than 34 sets is 0.71, determine the probability of selling 31, 32, or 33 sets.

• A0.5
• B0.29
• C0.21
• D0.08

Example

In a store selling computer sets, given that the probability of selling 31 sets at least daily is 0.79, and the probability of selling less than 34 sets is 0.71, determine the probability of selling 31, 32, or 33 sets.

Solution

The notation refers to the probability of either event or event occurring, or both. In this case, event is selling at least 31 computer sets daily, and event is selling less than 34 sets daily. Since and make up the sample space in this case, must be equal to 1. If and are two non-mutually exclusive events, then , where the notation refers to the probability of events and occurring together. Use this fact to determine .

Thus, the probability of selling 31, 32, or 33 computer sets is 0.5.

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