The scientist would use milligrams, grams, and kilograms.
The best procedure would be to randomly pick 52 fish from the entire pond and weigh each of them as this would be the most unbiased way to achieve the average mass
C.) 3:5 = 12:20
It is this because you can divide them evenly into each other. 3*4 is 12 and if you do 5*4 it is 20. Boo yeah