How would it be possible to cross a man that has Type B blood and a woman who has Type A blood, while their child has Type O blood?

Explanation:

For them to have a type o baby that means the man or woman must have a type o in there family some how to get passes down to the baby

If the parents are heterozygous for type A blod and for type B blood, when crossed, there is a 25% chance teh kid will have type O blood

Explanation: This is possible because there are two genotypes that code for type A and B blood

The genotypes for type A blood are:

I^A I^A     or     I^A i

The genotypes for type B blood are:

I^B I^B     or     I^B i

Visual: (Punnett square)

            I^A           i

I^B    I^A I^B     I^B i

i           I^A i         ii

*Remember that the genotype for type O blood is ii

i think its the first one

your spelling is a little off : ]