What's the probability that there are no more than 6 ​non-smartphone owners?

Question

According to a​ study, ​9% of teenagers​ (age 13-18) have a smartphone. Suppose eight teenagers are selected at random. What's the probability that there are no more than 6 ​non-smartphone owners?

Answer 1

Hi Mila F.,

Not such a hard problem. Just requires a little thought to set up. Let's suppose you picked the S's at random, then lined them up such that the dumbphoners stood first, then the smartphoners. So the problem asks, What is 1 - P(7 or 8 dumbphoners), right? So P(7 dumb, then 1 smart )=0.91^7 * 0.09 ; P(* dumb) = 0.91^8 . Which you calculated through, while the smartphoners were still asking "Alexa, if the probability of me or anyone else owning ... no wait, I already own one ...." Been there, I ask classes "If your phone is so smart, ask how many volcanos in the world have three double letters in their name"?

-- Cheers, -- Mr. d.