Answer: The probability of having an offspring with type A blood is 1/4.
Explanation: Since each of the parents have a recessive allele for blood type O, their genotypes are IAi and IBi for the father and mother respectively. A cross between them will produce four offsprings: one with type AB blood, one with type A blood, one with type B blood and one with type O blood.
See the attached punnet square for more information