The CAS Registry Mumber 83315-99-5 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, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 83315-99: (7*8)+(6*3)+(5*3)+(4*1)+(3*5)+(2*9)+(1*9)=135 135 % 10 = 5 So 83315-99-5 is a valid CAS Registry Number.