Why is it that the “number of ways that we can get an odd prime three times when a die is rolled five times” is 10! over 3! x 2!? Can someone explain it a little more for me? thanks! i understand the rest of the solution
5! not 10!
Yeah, sorry I meant 5!. But why is it 5! over 3! x 2!? I don’t get how this combinations is calculated
Recall that combinations (\binom{n}{r}) (i.e, not permutations) is
\binom{n}{r} = \frac{n!}{(n - r)! r!}
Does that help?
Hi, so we won’t be using permutations with repetitions (total!/repeat!) as shown in the Prep video?
You can do that if you want as well, by considering two outcomes: get a prime or not a prime. Think of it like this: let “get a prime” be X and “not a prime” be Y. Then you’re just arranging 3Xs and 3Ys.
Got it, thanks so much