The CAS Registry Mumber 7141-87-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,1,4 and 1 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 7141-87: (6*7)+(5*1)+(4*4)+(3*1)+(2*8)+(1*7)=89 89 % 10 = 9 So 7141-87-9 is a valid CAS Registry Number.