The CAS Registry Mumber 75980-09-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,9,8 and 0 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 75980-09: (7*7)+(6*5)+(5*9)+(4*8)+(3*0)+(2*0)+(1*9)=165 165 % 10 = 5 So 75980-09-5 is a valid CAS Registry Number.