Suppose you have monohybrid pea plants in your garden and find that they produce round seed to wrinkled seeds in the ratio of 3: 1. if the allele are designated (r & r) respectively, what is the probable genotypes of the round seeds which were produced

In a monohybrid cross, a 3:1 ratio indicates that both parents are heterozygous (Rr).  Since wrinkled is the recessive trait in this case, a seed must be homozygous for the recessive wrinkled allele (rr, with a probability off 25%).  Since round is dominant to wrinkled in this case, the round offspring have two options for their genotypes; heterozygous like the parents (Rr, with a probability of 50%) or homozygous for the dominant round allele (RR, with a probability of 25%).