The CAS Registry Mumber 3305-28-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,3,0 and 5 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 3305-28: (6*3)+(5*3)+(4*0)+(3*5)+(2*2)+(1*8)=60 60 % 10 = 0 So 3305-28-0 is a valid CAS Registry Number.