The CAS Registry Mumber 3855-89-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,8,5 and 5 respectively; the second part has 2 digits, 8 and 9 respectively. Calculate Digit Verification of CAS Registry Number 3855-89: (6*3)+(5*8)+(4*5)+(3*5)+(2*8)+(1*9)=118 118 % 10 = 8 So 3855-89-8 is a valid CAS Registry Number.