The boy has blood group I, and the girl has blood group IV. What about their parents’ blood types?

To understand what blood group the father and mother of the children have, it is necessary to use a special table, where the blood groups of the parents and the possible blood groups of the children are indicated. Also, many tables indicate the probabilities of a particular blood group in a child with known parent groups. This can be a probability of 0, 25, 50, 75, or 100%. If the children have the first and fourth blood groups, then one parent should have the third, and the other – the second group. Who has the second and third groups does not matter.

Answer: ІІ and ІІІ groups.