The CAS Registry Mumber 87281-85-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,2,8 and 1 respectively; the second part has 2 digits, 8 and 5 respectively. Calculate Digit Verification of CAS Registry Number 87281-85: (7*8)+(6*7)+(5*2)+(4*8)+(3*1)+(2*8)+(1*5)=164 164 % 10 = 4 So 87281-85-4 is a valid CAS Registry Number.