The CAS Registry Mumber 128779-89-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,7,7 and 9 respectively; the second part has 2 digits, 8 and 9 respectively. Calculate Digit Verification of CAS Registry Number 128779-89: (8*1)+(7*2)+(6*8)+(5*7)+(4*7)+(3*9)+(2*8)+(1*9)=185 185 % 10 = 5 So 128779-89-5 is a valid CAS Registry Number.