The CAS Registry Mumber 124218-91-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,4,2,1 and 8 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 124218-91: (8*1)+(7*2)+(6*4)+(5*2)+(4*1)+(3*8)+(2*9)+(1*1)=103 103 % 10 = 3 So 124218-91-3 is a valid CAS Registry Number.