Question
Suppose the following facts to be true: The probability of a random kindergartener having chicken pox at any given time is 2%. Among kindergarteners who have chicken pox, 75% have red spots. Among kindergarteners who do not have chicken pox, 1% have red spots. Given that Sanjay, a kindergartener, has red spots, what is the probability that Sanjay has chicken pox? Enter your answer as a fraction in simplified form.
Answer:
75/124
Explanation:
This is a question based on conditional Probability
We would solve this using Bayes's Theorem of Conditional Probability
From the above question, we have the following information:
The probability of a random kindergartener having chicken pox at any given time is 2%.
Hence, the probability that a kindergartner would not have chicken pox
= 100% - 2%
= 98%
Kindergarteners who have chicken pox, 75% have red spots.
Kindergarteners who do not have chicken pox, 1% have red spots.
The Sanjay, a kindergartener, has red spots, the probability that Sanjay has chicken pox is calculated as:
= (Probability of a random kindergartener having chicken pox at any given time ⋂ Probability of kindergarteners who have chicken pox, and have red spots)/ [(Probability of a random kindergartener having chicken pox at any given time ⋂ Probability of kindergarteners who have chicken pox, and have red spots) + (Probability Kindergarteners who do not have chicken pox and have red spots ⋂ Probability that a kindergartner would not have chicken pox)
= (2% × 75%)/[(2% × 75%) +( 1% × 98%)]
= 150/150 + 98
= 150/248
= 75/124