math
posted by Shawn on .
selecting three (3) coins, but assume that there are 5 dimes, 4 nickels, and 2 quarters.
In how many possible ways can the selection be made so that the value of the coins is at least 25 cents?

The only possible cases are, hope I did not miss any
DDD  30
DDN  25
DDQ  45
DNN  20
DNQ  40
DQQ  60
NNN  15
NNQ  35
NQQ  55
How many of these amount to at least 25 cents?
(notice that the fact that we have 5 dimes and 4 nickels is of no consequence, since we can use at most 3, but the 2 quarters limits the cases)