Mrs. Blue and Mrs. Green had babies at the same hospital and at the same time. Mrs. Blue took home a girl and named her Nancy. Mrs. Green took home a boy and named him John. However, Mrs. Green was sure she had a girl and brought suit against the hospital. Blood tests showed that Mr. Green was type O, Mrs. Green was type AB, and Mr. and Mrs. Blue were both type B. Nancy was type A, and John was type O. Required:
Was there a mix-up at the hospital?