The CAS Registry Mumber 987-07-5 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 9,8 and 7 respectively; the second part has 2 digits, 0 and 7 respectively. Calculate Digit Verification of CAS Registry Number 987-07: (5*9)+(4*8)+(3*7)+(2*0)+(1*7)=105 105 % 10 = 5 So 987-07-5 is a valid CAS Registry Number.