The CAS Registry Mumber 87281-90-1 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, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 87281-90: (7*8)+(6*7)+(5*2)+(4*8)+(3*1)+(2*9)+(1*0)=161 161 % 10 = 1 So 87281-90-1 is a valid CAS Registry Number.