A large sack contains six basketballs and five volleyballs. Find the number of combinations of four b***s that can be chosen from the sack if: a) They may be any type of ball b) Two must be volleyballs and two must be basketballs c) All four must be volleyballs d) None may be volleyballs
Since there is 6 basketballs and 5 volley b***s this is the best way to find the answer:
[(6C0)(5C4)]+[(6C1)(5C3)]+[(6C2)(5C2)]+[(6C3)(5C1)]+[(6C4)(5C0)] = 330
Basically what I did was find out when ther was 0 basketballs and 5 volleyballs, 1 basketball and 4 volleyballs, 2 basketballs and 3 volleyballs, and so forth.
So the answers is 330.
I had to think a lot on this question too, a helpful tip when doing questions like this is to make sure you understand the question before you write anything down.
Glad I could help!