How many ways are there to place 7 balls in 14 boxes. Balls are numbered from 1 to 7. One box can contain only one ball. And out of 14 boxes atleast 6 boxes must contain first 6 balls. 7th ball is optional either you may put it in boxes or not.
Please explain how to solve these types of question and what approach should I use. Also if the number of boxes was 1 or 2 or 100 what approach should I use?