A large pile of coins consists of pennies, nickels, dimes and quarters.
a) How many different collections of 30 coins can be chosen if there are at least 30 of each kind of coin?
b) If the pile contains only 15 quarters but at least 30 of each other kind of coin, how many collections of 30 coins can be chosen?
Is the answer to part (a) C(30,4)? What about part (b)?