Answer:
25%
Explanation:
If a mother of blood type AB has children with father of blood type BO than there is a 25% chance that they had a child with blood type AB.
As the mother has two alleles A and B.
Father has two alleles B and O. So there are total of 4 sequences AB, AO, B, and BO.
AB 25%
AO 25%
B 25%
BO 25%