The CAS Registry Mumber 100009-74-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,0,0 and 9 respectively; the second part has 2 digits, 7 and 4 respectively. Calculate Digit Verification of CAS Registry Number 100009-74: (8*1)+(7*0)+(6*0)+(5*0)+(4*0)+(3*9)+(2*7)+(1*4)=53 53 % 10 = 3 So 100009-74-3 is a valid CAS Registry Number.