The CAS Registry Mumber 80035-66-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,0,3 and 5 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 80035-66: (7*8)+(6*0)+(5*0)+(4*3)+(3*5)+(2*6)+(1*6)=101 101 % 10 = 1 So 80035-66-1 is a valid CAS Registry Number.