The CAS Registry Mumber 91281-69-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,2,8 and 1 respectively; the second part has 2 digits, 6 and 9 respectively. Calculate Digit Verification of CAS Registry Number 91281-69: (7*9)+(6*1)+(5*2)+(4*8)+(3*1)+(2*6)+(1*9)=135 135 % 10 = 5 So 91281-69-5 is a valid CAS Registry Number.