I was given a very strange problem with not really much information but still thinking about it, here it goes:
If 100 persons that enter a store and 70 from those buy something and 30 don't buy anything. Find the probability that if 10 persons enter the store, that 3 of them won't buy anything.
I thought it was with Moivre-Laplace and to find the probability of $P(X_k< 3)$ but that would be if at most 3 won't buy anything and I think i need if exactly $3$ don't buy anything. What should I do?
It seems that the first sentence gives us the information about the (fixed) proportion of buying people, which is $p=0.7$
Let X the random variable of people who buy something, then it is binomial distributed as $X\sim Bin(10, 0.7)$
The question just ask for the probability that 7 (of 10) people buy something, which is $P(X=7)=...$. There is no Moivre-Laplace needed.
Do you comprehend my thoughts and can you proceed?