A standard six-sided die is rolled $7$ times. You are told that among the rolls, there was one $1,$ one $2$, one $3$, one $4$, one $5$, and two $6$s. How many possible sequences of rolls could there have been? (For example, 2, 3, 4, 6, 6, 1, 5 is one possible sequence.)
To find the total sequences just find how many ways there are to order 1, 2, 3, 4, 5, 6, 6.
This is 7!/2! = 2520