Hey everyone I had difficulties while solving this problem in probability. We have 4 similar boxes, and 20 similar balls. How many possible ways we can put those balls on those boxes, knowing that -the first box contains 3 balls - the second box contains 4 balls - the third box contains 6 balls - and the fourth box contains 7 balls What I did, is since we have 4 boxes, it's going to be 4! in the first box it's 3! and second, third and fourth i also 4!*6!*7! So is the number of ways we can diperse those balls: 4!*4!*6!*7! ??? The secong problem stats: How many 3-digits numbers we have that that contains 2 similar digits! For this one, I have NO clue how to proceed. Thanks for your help!