How many ways are there to pick a collection of 12 coins from piles of pennies, nickels, dimes, and quarters?
a) Assuming that each pile has at least 12 or more coins.
For this one, I got CR(4,12) = C(4+11,12) = C(15,12) = 15! divided by(12!) and 3! = 455
b) Assuming that each pile has at least 12 or more coins and the pick must consist of at least one quarter coin or at least one dime.
For this one, I did 12 choose 4 minus 10 choose 2 to get 450.
Are those right? Any help would be appreciated! Thanks!