The CAS Registry Mumber 109273-55-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,2,7 and 3 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 109273-55: (8*1)+(7*0)+(6*9)+(5*2)+(4*7)+(3*3)+(2*5)+(1*5)=124 124 % 10 = 4 So 109273-55-4 is a valid CAS Registry Number.