The CAS Registry Mumber 5309-99-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,3,0 and 9 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 5309-99: (6*5)+(5*3)+(4*0)+(3*9)+(2*9)+(1*9)=99 99 % 10 = 9 So 5309-99-9 is a valid CAS Registry Number.