Answer:
0%
Step-by-step explanation:
Let's use a Punnett square to solve this problem.
A B
O AO BO
O AO BO
The Punnett square shows that 50% of their children will have the AO genotype and 50% will have the BO genotype. Neither of these genotypes give the child type O blood, so it is impossible for the child to have type O blood. The child would need two O alleles.