Question

Before each class, I either drink a cup of coffee, a cup of tea, or a cup of water. The probability of coffee is 0.7, the probability of tea is 0.2, and the probability of water is 0.1. If I drink coffee, the probability that the lecture ends early is 0.3. If I drink tea, the probability that the lecture ends early is 0.2. If I drink water, the lecture never ends early. 1) What’s the probability that I drink tea and finish the lecture early? 2) What’s the probability that I finish the lecture early? 3) Given the lecture finishes early, what’s the probability I drank coffee?

Answer 1

Answer:

1. Probability of drinking tea and finishing the lecture early = 0.2 * 0.2 = 0.04 or 4%

2. Probability of finishing the lecture early = 50% (0.3 + 0.2).

3. Probability of drinking coffee = 0.21 or 21% (0.7 * 0.3)

Step-by-step explanation:

a) Data and Calculations:

            Probability   Early Ending    Expected Probability

Coffee     0.7               0.3                     0.21

Tea          0.2               0.2                    0.04

Water      0.1                

b) The probability of drinking coffee, tea, or water is the chance that the lecturer drinks either coffee or tea or water.  The combined probability of the three actions is always 1.  The expected probability is the weighing of the probabilities with another event, ending the lecture early.  This is obtained by multiplying their respective probabilities.