there are 15 ducks swimming in a pond. If 3/5 of the ducks are males, how many female ducks are swimming in the pond?

If 3/5 of the ducks are males, then 2/5 of the ducks are females.

The number of female ducks is 2/5*15 ducks = <<2/5*15=6>>6 ducks. Answer: \boxed{6}.