The CAS Registry Mumber 109157-85-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,1,5 and 7 respectively; the second part has 2 digits, 8 and 5 respectively. Calculate Digit Verification of CAS Registry Number 109157-85: (8*1)+(7*0)+(6*9)+(5*1)+(4*5)+(3*7)+(2*8)+(1*5)=129 129 % 10 = 9 So 109157-85-9 is a valid CAS Registry Number.