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Help with Combinations!!!!!!
(C(13,4)  (C(7,4)*C(6,4)))/(C(13,4)
 one year ago
 one year ago
Help with Combinations!!!!!! (C(13,4)  (C(7,4)*C(6,4)))/(C(13,4)
 one year ago
 one year ago

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KingGeorgeBest ResponseYou've already chosen the best response.1
Do you know the formula for what C(n,k) is?
 one year ago

dreadslicerBest ResponseYou've already chosen the best response.0
n!/((nr)!r!) n=13 r=4 =715 n=7 r=4 =35 n=6 r=4 =15
 one year ago

nishathompBest ResponseYou've already chosen the best response.0
n is the pool or what you are choosing from and k is the select or the amount you can take
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
Basically that's what it it is. But as dreadslicer pointed out above, the formula for C(n,k) is\[C(n,k)=\frac{n!}{k!(nk)!}\]Using this, you can individually calculate the different values you need. Since you need to find \[\frac{C(13,4)C(7,4)\cdot C(7,3)}{C(13,4)}\]You need only to find C(13,4), C(7,4), and C(7,3). Can you list these out for me?
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
Looks correct to me. Now you just simplify that as much as you can.
 one year ago

nishathompBest ResponseYou've already chosen the best response.0
yeah but when i do i get the wrong answer :[
 one year ago

nishathompBest ResponseYou've already chosen the best response.0
the whole problem is this : JeanLuc's starship encounters an enemy starship. After realizing that he had no choice but to get, JeanLuc orders his weapons ocer to re 4 weapons at the enemy starship. The weapons ocer randomly selects the 4 weapons to re from a total of 6 photon torpedoes and 7 positron torpedoes. What is the probability that officer selected torpedoes of both types?
 one year ago

nishathompBest ResponseYou've already chosen the best response.0
i thought i could take the compliment... did i do it right?
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
You nearly had it. Just instead of multiplying C(7,4) and C(6,4), subtract both of them. So your equation should be \[\frac{C(13,4)C(7,4)C(7,3)}{C(13,4)}\]You take out the choices where you choose all positron torpedoes, and then take out the choices where you chose only photon torpedoes. Then you divide by the total.
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
And that should be a C(6,4) not a C(7,3). Sorry about that...
 one year ago

nishathompBest ResponseYou've already chosen the best response.0
ohhhh you subtract them? i thought i could combine them by multiplying them. is there anyreason as to why i couldnt do that?
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
Basically, you have two cases. Case 1, all positron torpedoes. Case 2, all photon torpedoes. When you have two distinct cases like this, you have to add/subtract.
 one year ago

KingGeorgeBest ResponseYou've already chosen the best response.1
And I've got to go now, feel free to ask more questions as a response, and I'll take a look later tonight.
 one year ago
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