The CAS Registry Mumber 83315-81-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,3,1 and 5 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 83315-81: (7*8)+(6*3)+(5*3)+(4*1)+(3*5)+(2*8)+(1*1)=125 125 % 10 = 5 So 83315-81-5 is a valid CAS Registry Number.