Question

There are 9 red checkers and 3 black checkers in a bag. Checkers are selected one at a time, with replacement. Each time, the color of the checkers is recorded. Find the probability of selecting a red checker exactly 9 times in 15 selections.
Please explain... :/
Thanks!
This is what I have so far:
p=red=9/15=.6
n=9
???

Answer 1

You are on the right track...
There are a total of 12 checkers in the bag, 9 of which are red, the probability of use picking a red one is 9/12. So if we want to find the probability that we will draw a red checker 9 times and black checker 6 times since total drawings is 15, we use:

P(R,R,R,R,R,R,R,R,R,B,B,B) this says we draw 9 red and 3 black in 15 draws, so...

We can do
(9/12)(9/12)(9/12)(9/12)(9/12)(9/12)(9/12)(9/12)(9/12)(3/12)(3/12)(3/12)=P

Multiplying those together will get you your overall probability that you draw a red 9 times and black 3 times.