Question

A pea plant with round seeds has the genotype rr. if you cross this plant with a wrinkled-seed plant, genotype rr, what is the probability that the offspring will have wrinkled seeds?

Answer 1

I think you wrote this wrong? Is it not round rr vs wrinkled RR?? I'll answer it with that assumption:

You are crossing a rr with an RR:
You only get Rr back so they will phenotypically be all wrinkled

If you are crossing rr with an Rr (so a heterozygote wrinkled):
50% will be Rr (wrinkled)
50% will be rr (round)
See my picture for the Punnett Squares for both answers!