How many ways are there to put 6 balls in 3 boxes if the balls are not distinguishable but the boxes are?
Look at solution #10 here:
https://web2.0calc.com/questions/how-many-ways-are-there-to-put-6-balls-in-3-boxes-if-the-balls-are-distinguishable-and-the-boxes-are-distinguishable
Anybody who is interested in this type of question can visit this page which gives very extensive details about the restrictions and a variety of formulas to solve them. Some of them are quite advanced, requiring knowledge of "partitions", "Stirling numbers of the second kind!"........etc.
https://www.careerbless.com/aptitude/qa/permutations_combinations_imp7.php
