We will use the Hardy-Weinberg equation ; p2 + 2pq + q2 = 1 q2 represent the frequency of the recessive trait in the population which is 400/10000 = 0.04. Then find frequency of the recessive allele. q = 0.2. While we understand that p+q =1 ; p = 1-q ; p = 1-0.2 =0.8. 2pq represents the frequency of heterozygous trait in the population. Therefore 2*0.8*0.2 =0.32 0.32*10000 = 3200
