The CAS Registry Mumber 788-87-4 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,8 and 8 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 788-87: (5*7)+(4*8)+(3*8)+(2*8)+(1*7)=114 114 % 10 = 4 So 788-87-4 is a valid CAS Registry Number.