How many different four figure numbers can be made using the digits 1 9 9 1?

4!/(2!*2!) = 4*3*2*1/(2*1*2*1) = 6

4!/(2!*2!) = 4*3*2*1/(2*1*2*1) = 6

4!/(2!*2!) = 4*3*2*1/(2*1*2*1) = 6

4!/(2!*2!) = 4*3*2*1/(2*1*2*1) = 6