In a hypothetical population of 1000 frogs there exists a gene, d, with two alleles (d and d). 280 of the frogs are homozygous dominant (dd), and 220 are homozygous recessive (dd). what is the frequency of heterozygotes in the population?

To answer this question, subtract from the total population of 1000 the homozygous dominant (DD) frogs of 280 and the homozygous recessive (dd) frogs of 220, and you are left with 500 frogs that by default are heterozygotes (dD). The frequency of these frogs would be 500/1000 = 0.5