The CAS Registry Mumber 307-09-5 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 3,0 and 7 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 307-09: (5*3)+(4*0)+(3*7)+(2*0)+(1*9)=45 45 % 10 = 5 So 307-09-5 is a valid CAS Registry Number.