##### My Question
AZobi
Hopefully this a worthy enough question: A bag contains 4 blue balls and 5 yellow balls. You take three balls out without returning them to the bag. In how many ways can you pick out three balls of the same color?
weisbart: Feb. 1, 2015, 8:51 a.m.
It is a worthy question! Is anyone brave enough to try it? Then you can try and rate it: A level difficulty, B level, or C level. I'm curious to know what the consensus is. AZobi, at what level would you rate it and why? Well, you'll probably have to wait until someone gives an answer as you might give it away.
AZobi: Feb. 1, 2015, 11:25 p.m.
Will do! Also, I noticed that I accidentally posted this question under the wrong section. I will repost it as to avoid benefiting simply because no one saw my post.
Joyce2E: Feb. 4, 2015, 1:07 p.m.
JUST GIVE IT A TRY: 14 if simultaneously? 84 if separately?
AZobi: Feb. 4, 2015, 7:56 p.m.
14 is correct :)
weisbart: Feb. 5, 2015, 7:36 p.m.
Joyce2E: Feb. 6, 2015, 12:15 a.m.
Well, In order to choose 3 balls of the same color at the same time, for the 4 blue ones, you have(4 choose 3) ways to choose from; similarly for the 5 yellow ones, you have(5 choose 3) ways to choose from. Since the two different cases corresponds to disjoint subsets, you have to add the numbers. ^.^
AZobi: Feb. 6, 2015, 4:35 p.m.
Joyce2E, you're explanation matches mine.
weisbart: Feb. 6, 2015, 8:26 p.m.