The CAS Registry Mumber 88905-18-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,8,9,0 and 5 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 88905-18: (7*8)+(6*8)+(5*9)+(4*0)+(3*5)+(2*1)+(1*8)=174 174 % 10 = 4 So 88905-18-4 is a valid CAS Registry Number.