The CAS Registry Mumber 97800-79-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,7,8,0 and 0 respectively; the second part has 2 digits, 7 and 9 respectively. Calculate Digit Verification of CAS Registry Number 97800-79: (7*9)+(6*7)+(5*8)+(4*0)+(3*0)+(2*7)+(1*9)=168 168 % 10 = 8 So 97800-79-8 is a valid CAS Registry Number.