The CAS Registry Mumber 97800-80-1 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, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 97800-80: (7*9)+(6*7)+(5*8)+(4*0)+(3*0)+(2*8)+(1*0)=161 161 % 10 = 1 So 97800-80-1 is a valid CAS Registry Number.