Introductory Statistics 9th Edition

Published by Wiley
ISBN 10: 1-11905-571-7
ISBN 13: 978-1-11905-571-6

Chapter 4 - Section 4.3 - Marginal Probability, Conditional Probability, and Related Probability Concepts - Exercises - Page 149: 4.29

Answer

Marginal probability is the probability of a single event without consideration of any other event. For example, The table given shows the distribution of 100 workers based on two characteristics: gender (male or female) and hobby (reading or swimming). One worker is selected at random from these 100 workers. The marginal probablities are calculated as follows: P(male) = $\frac{Number of male workers}{Total number of workers} = \frac{50}{100} = 0.5$ P(female) = $\frac{Number of female workers}{Total number of workers} = \frac{50}{100} = 0.5$ P(reading) = $\frac{40}{100} = 0.4$ P(swimming) = $\frac{60}{100} = 0.6$ Conditional probability is the probability that an event will occur given that another event has already occurred. If A and B are two events, then the conditional probability of A given B is written as: P(A|B). For example: According to the table, P(reading|female) = $\frac{30}{50} = 0.6$ P(swimming|male) = $\frac{40}{50} = 0.8$ The probability P(reading|female) and P(swimming|male) are the conditional probability that a randomly selected worker is reading (or swimming) given that this worker is a female (or male).

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