The CAS Registry Mumber 90105-85-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,0,1,0 and 5 respectively; the second part has 2 digits, 8 and 5 respectively. Calculate Digit Verification of CAS Registry Number 90105-85: (7*9)+(6*0)+(5*1)+(4*0)+(3*5)+(2*8)+(1*5)=104 104 % 10 = 4 So 90105-85-4 is a valid CAS Registry Number.