You have 3 types of postcards. There are 5 of each type. How many ways can you send the 15 postcards to 15 friends, if each friend receives 1.
The Attempt at a Solution
I thought it would merely be 15!/(3*5!)
it's because it has to be multiplied. For every rearrangement of five identicals, there are two more rearrangements of the others