How many sets of five-digit numbers formed by the digits 1,6,8,5 and 1,?

Question

How many sets of five-digit numbers formed by the digits 1,6,8,5 and 1,?

Answer 1

5! / 2! = 5•4•3 = 60

5! arrangements of 5 distinct things, divide by 2! arrangements of 2 identical 1's.  

Answer 2

5! / 2!

= (5 x 4 x 3 x 2 x 1) / (2 x 1)

= 60