How many ways can you get three 4's and two 1's in 5 die rolls?

120/(6)(2)=10 ways. There 120 ways (5!) to arrange 5 different objects (5 die rolls).
But there are 6 ways of perming 3 different objects. But we need to discount the 120 by a factor of 6 because there is only one way to get 3 fours. Similarly we discount by a factor of 2 for the two ones. Total discount is 6×2=12. Therefore we divide 120 by 12 to get 10.