The CAS Registry Mumber 87033-42-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,0,3 and 3 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 87033-42: (7*8)+(6*7)+(5*0)+(4*3)+(3*3)+(2*4)+(1*2)=129 129 % 10 = 9 So 87033-42-9 is a valid CAS Registry Number.