Let the number of cats in a farm be [tex]x[/tex] and the number of rabbits be [tex]y[/tex]. The total number of cats and rabbits would be be [tex]x + y[/tex]. As the number of dogs in the farm are [tex]\frac{3}{5}^{th}[/tex] the total number of cats and rabbits, so:
Number of dogs in the farm = [tex]\frac{3}{5} (x + y)[/tex]