The CAS Registry Mumber 109757-80-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,7,5 and 7 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 109757-80: (8*1)+(7*0)+(6*9)+(5*7)+(4*5)+(3*7)+(2*8)+(1*0)=154 154 % 10 = 4 So 109757-80-4 is a valid CAS Registry Number.