The CAS Registry Mumber 31883-85-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,1,8,8 and 3 respectively; the second part has 2 digits, 8 and 5 respectively. Calculate Digit Verification of CAS Registry Number 31883-85: (7*3)+(6*1)+(5*8)+(4*8)+(3*3)+(2*8)+(1*5)=129 129 % 10 = 9 So 31883-85-9 is a valid CAS Registry Number.