The CAS Registry Mumber 86870-91-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,6,8,7 and 0 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 86870-91: (7*8)+(6*6)+(5*8)+(4*7)+(3*0)+(2*9)+(1*1)=179 179 % 10 = 9 So 86870-91-9 is a valid CAS Registry Number.