The CAS Registry Mumber 87424-87-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,4,2 and 4 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 87424-87: (7*8)+(6*7)+(5*4)+(4*2)+(3*4)+(2*8)+(1*7)=161 161 % 10 = 1 So 87424-87-1 is a valid CAS Registry Number.