YouTube is a popular destination on the internet; let\'s look at how YouTube usa

Question

YouTube is a popular destination on the internet; let's look at how YouTube usage is distributed among age groups. According to the Pew Internet and American Life Project, about 70% of internet users aged 18-29 have visited YouTube, along with 51% of those aged 30-49 and 26% of those 50 or older. About 23% of adult internet users are 18-29 years old, another 45% are 30-49, and the remaining 32% are 50 and over.

(a) Calculate the probability that a randomly selected internet user has used YouTube.


(b) If we randomly select a YouTube internet user, what is the probability they are aged 18-25?

Explanation / Answer

a. P(internet user has used YouTube) = P(age = 18-29) * P(youtube | age = 18-29) + P(age = 30-49) * P(youtube | age = 30-49) + P(age >= 50) * P(youtube | age >= 50)

= 0.23 * 0.7 + 0.45 * 0.51 + 0.32 * 26 = 0.474

b. P(age = 18-29 | youtube) = P(age = 18-29) * P(youtube | age = 18-29) / P(internet user has used YouTube)

= 0.23*0.7 / 0.474 = 0.34

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