Answer:
The answer is 455 ways.
Step-by-step explanation:
If adding only twelve, you must leave out three of the fifteen, and the number of ways is = 15! / (3! * 12!).
1∗2∗3∗4∗5∗6∗6∗8∗9∗10∗11∗12∗13∗14∗15 over
(1∗2∗3)∗(1∗2∗3∗4∗5∗6∗6∗8∗9∗10∗11∗12) =
13∗14∗15 over
(1∗2∗3)
27306 = 455
