The CAS Registry Mumber 109879-75-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,8,7 and 9 respectively; the second part has 2 digits, 7 and 5 respectively. Calculate Digit Verification of CAS Registry Number 109879-75: (8*1)+(7*0)+(6*9)+(5*8)+(4*7)+(3*9)+(2*7)+(1*5)=176 176 % 10 = 6 So 109879-75-6 is a valid CAS Registry Number.