The CAS Registry Mumber 124218-87-7 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, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 124218-87: (8*1)+(7*2)+(6*4)+(5*2)+(4*1)+(3*8)+(2*8)+(1*7)=107 107 % 10 = 7 So 124218-87-7 is a valid CAS Registry Number.