The CAS Registry Mumber 108998-91-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,9,9 and 8 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 108998-91: (8*1)+(7*0)+(6*8)+(5*9)+(4*9)+(3*8)+(2*9)+(1*1)=180 180 % 10 = 0 So 108998-91-0 is a valid CAS Registry Number.