The CAS Registry Mumber 83169-55-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,1,6 and 9 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 83169-55: (7*8)+(6*3)+(5*1)+(4*6)+(3*9)+(2*5)+(1*5)=145 145 % 10 = 5 So 83169-55-5 is a valid CAS Registry Number.