Answer:
The number of ducks are 9.
Step-by-step explanation:
There are x ducks in a pond.
The number of swans in the pond is equal to the square root of the number of ducks.
Means swans = 
If the total number of swans and ducks in the pond is 12.

=> 
Squaring both sides, we get

=> Taking everything on one side and equating to 0

=> 
=> Solving this we get, x = 9 and x = -16
So, we have number of ducks as 9.
And number of swans = 