Sagot :
Step-by-step explanation:
When they ask what the prob that at most 3/4 people asked have a pet, they are asking what is the prob that 0, 1, 2, or 3 people answer yes. So you could calculate all 4 of those and then add them together.
However, in this case, since there's only 1 other possible outcome (all 4 have a pet), we could just calculate the prob of that and subtract it from 1 to get the prob of everything else happening.
We'll use the binomial distribution formula where n=4, k=4, and P=.6.
nCk * P^n * (1-P)^(n-k)4C4 * (.6)^4 * (.4)^0.1296
So the prob of at least 3 having pets = 1 - P(all 4 have pets) which is 1-.1296 = .8704. You could double check this by calculating the prob of the other 4 outcomes and then adding them together.