How do you calculate stream gradient?

a. horizontal distance minus elevation difference

b. elevation difference divided by horizontal distance

c. elevation difference times horizontal distance

d. horizontal distance divided by elevation difference

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.