Human blood can contain either no antigens, the A antigen, the B antigen or both the A and B antigens. A third antigen, called the Rh antigen is significant in human reproduction and again may or may not be present in an individual. Blood is called type A positive if the subject has the A and Rh, but not the B antigen. Subjects having only the A and B antigens are said to have type AB - negative blood. Subjects having only the Rh antigen have type O - positive blood, etc. In a certain hospital the following data on patients were recorded; 25 patients had the A antigen 17 had the A and B antigens 27 had the B antigen 22 had the B and Rh antigens 30 had the Rh antigen 12 had none of the antigens 16 had the A and Rh antigens 15 had all the three antigens Required: How may patients?