Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith took home a baby girl, whom she named Sharon. Mrs. Jones took home a girl, whom she named Jane. Mrs. Jones began to suspect, however, that the child had been accidentally switched with Mrs. Smith baby in the nursery. Blood test were made; Mr. Smith was type A, Mrs. Smith was type B, Mr. Jones was type A, Mrs. Jones was type A. Sharon was type O, and Jane was type B. Had a mix-up occurred?