Given: Three positive integers k, m, and n, representing a population containing k + m + n organisms: k individuals are homozygous dominant for a factor, m are heterozygous, and n are homozygous recessive.
Return: The probability that two randomly selected mating organisms will produce an individual possessing a dominant allele (and thus displaying the dominant phenotype). Assume that any two organisms can mate.
Note: formula derived on paper
