probabilities and statistics: 4 yellow, 8 blue marbles

[dedwards]

from 4 yellow and 8 blue marbles, 3 are selected. What is the probability that all three are yellow or all three are blue?

please give me a step to step on how to master this problem, i am so confused i dont know where to start.

 

[galactus]

Re: probabilities and statistics...

Notice the OR statement. We know that P(Y or B)=P(Y)+P(B)-P(Y and B)

In this case, P(Y and B)=0 because they are mutually exclusive. Ask yourself, "Can I draw a yellow and blue at the same time?"

No, you can not. So, they are mutually exclusive.

Let Y be the yellow marbles and B be the blue marbles.

The probability of drawing 3 yellows is (4/12)(3/11)(2/10). See why?.

Can you do the same for the blues?. Then add the two cases. Let me know what you get.