The CAS Registry Mumber 727-20-8 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,2 and 7 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 727-20: (5*7)+(4*2)+(3*7)+(2*2)+(1*0)=68 68 % 10 = 8 So 727-20-8 is a valid CAS Registry Number.