this might seem easy but i am easily confused.
Find the number of ways that Magnus can give out 10 identical stickers to 3 of his friends. (Not everyone has to get a sticker.)
There are 10 ways to choose which friend gets the first sticker, 9 ways to choose which friend gets the second sticker, and 8 ways to choose which friend gets the third sticker. However, we have overcounted the number of ways, since we have counted each possible distribution of stickers three times. Therefore, the number of ways to give out 10 stickers to 3 friends is 10×9×8/3! = 168.