QR topscore

[Doctor PJ]

---

Members don't see this ad.

can anyone show me how to work this problem. What is the probability of selecting 3 black cards out of a deck? Answer is 0.12. Not sure how to work this.

Another problem: what is the third term expansion of (x+3)^5? Answer is 90x^3

 

[Mstoothlady2012]

A deck has 52 cards, out of which 26 are black and 26 are red. So the probability of pick 3 black cards would be 3/26 = 0.12

 

[klutzy1987]

can anyone show me how to work this problem. What is the probability of selecting 3 black cards out of a deck? Answer is 0.12. Not sure how to work this.

The way to do this is 26/52 * 25/51 * 24/50

The reason for this is because after each selection there is one less black card and one less card in total. Therefore the first time there is a 25/52 shot because there are 26 black out of 52 total cards. The next one there are 25 black outa 51 total cards and the next is 24 black outa 50 total cards. That should be the answer. i havent calculated yet.

 

[Mstoothlady2012]

The way to do this is 26/52 * 25/51 * 24/50

The reason for this is because after each selection there is one less black card and one less card in total. Therefore the first time there is a 25/52 shot because there are 26 black out of 52 total cards. The next one there are 25 black outa 51 total cards and the next is 24 black outa 50 total cards. That should be the answer. i havent calculated yet.

So if the question said what is the probability of selecting 3 yellow marbles out 3 yellow marbles and 3 red marbles?

You would do (3/6) (2/5) (1/4) = 0.05

And not 3/6 = 0.5?

 

[klutzy1987]

exactly.

 

[futuredentist21]

Thank you klutzy!!! I always get these probability questions wrong

 

[Mstoothlady2012]

I always get confused between which one to pick when question like that shows up. When the question states clearly that you are picking one card after another, then I would do the solution that you gave. But when the question doesn't say that I just assume that you are grabbing all 3 cards at the same time. Uh! how do you knoww????

 

[flycd05]

The way to do this is 26/52 * 25/51 * 24/50

The reason for this is because after each selection there is one less black card and one less card in total. Therefore the first time there is a 25/52 shot because there are 26 black out of 52 total cards. The next one there are 25 black outa 51 total cards and the next is 24 black outa 50 total cards. That should be the answer. i havent calculated yet.

is this a permutation since order matters? if so, then how would u set it up using nPr...is n = 52 or 26 and then is r=3?

 

[klutzy1987]

Even if you are grabbing all three cards at the same time it would still be the same ( at least i think it would be im not sure if it would be considered as replacement, howeveri think it is the same). Either way, it wouldnt be a half because according to your logic the prob. of getting all 3 yellow is 3/6 and the prob. of getting 3 red is 3/6 so the prob. of getting any other combination of balls would be 0. That is obviously wrong. The answer there would still be 3/6 *2/5 * 1/4

 

[klutzy1987]

is this a permutation since order matters? if so, then how would u set it up using nPr...is n = 52 or 26 and then is r=3?

No its not a permutation it is basic multiplication of multiple probabilities. The permutation would be (26p3)/(52p3). That way is much more difficult and it would be silly to solve that way.