Solution:
Total number of Ducks = 3 Black + 3 White = 6 Ducks
Total Favorable Outcome = 2 White + 1 Black
Total Possible Outcome = Selecting 3 Ducks (2 White +1 Black) from 6 Ducks
Formula to Calculate Probability
= 
Use ,C(n,r)=
Probability of two white ducks one black duck swimming together
=
Simulation Using Coin Flip
H→White duck, T→Black Duck
HHH→Three White Ducks Sailing together
TTT→Three black ducks Sailing together
HHT→Two white duck and a Black Duck sailing together
HTH→Two white duck and a Black Duck sailing together
THH→Two white duck and a Black Duck sailing together
TTH→Two Black duck and a White Duck sailing together
THT→Two Black duck and a White Duck sailing together
HTT→Two Black duck and a White Duck sailing together
Other than coin which is used here for simulation, you can use Two different colored balls each being three in number.