- #1
daleklama
- 33
- 0
Homework Statement
Suppose 5 cards are dealt at random from a well shuffled, 52 card deck. The hand can be thought of as a random sample size 5 from 52, with no replacement.
What is:
(a) P (4 aces)
(b) P (3 aces and 2 kings)
(c) P (4 of a kind)
Homework Equations
I know the formula for 'combinations' (number of equally likely unordered outcomes, no replacement) is
number of equally likely unordered outcomes = n CHOOSE k, where n is the total sample size and k is the amount you're sampling/taking out.
The Attempt at a Solution
I know all of the solutions, I got them from my teacher, I just can't understand them at all!
These are the solutions:
(a) P (4 aces) = (4 choose 4) x (48 choose 1) / (52 choose 5)
(b) P (3 aces and 2 kings) = (4 choose 3) x (4 choose 2) / (52 choose 5)
(c) P (4 of a kind) = (13 choose 1) x (4 choose 4) x (48 choose 1) / (52 choose 5)
(a) I thought I understood this. I see why you'd put (52 choose 5) on the bottom, since that's what you're doing overall. And I thought it was (4 choose 4) because you have a total of 4 aces and you want all 4 of them, and I thought it was (48 choose 1) because you have 48 cards left to choose from, and you only need 1.
Is this right?
(b) Again, I kind of understand this, applying my previous logic. You have 4 aces and need 3, you have 4 kings and need 2, and that's your total hand dealt, so you don't need any more.
(c) I have no idea where this comes from.
Any help would be greatly appreciated!