The CAS Registry Mumber 81109-24-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,1,0 and 9 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 81109-24: (7*8)+(6*1)+(5*1)+(4*0)+(3*9)+(2*2)+(1*4)=102 102 % 10 = 2 So 81109-24-2 is a valid CAS Registry Number.