A man with type a blood whose mother was type o is married to a women with type ab blood what are the blood types of their children and in what proportion

Establish genotype/phenotype table

Genotype Phenotype

oo type O

AB type AB

Ao type A

Bo type B

So if parents' phenotypes are O and AB, then we can construct the Punnett square:

O O

A AO AO

B BO BO

So we conclude that the offsprings have phenotypes and proportions

type A (AO) 50%

type B (BO) 50%