The CAS Registry Mumber 3120-09-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,1,2 and 0 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 3120-09: (6*3)+(5*1)+(4*2)+(3*0)+(2*0)+(1*9)=40 40 % 10 = 0 So 3120-09-0 is a valid CAS Registry Number.