The CAS Registry Mumber 5548-55-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,5,4 and 8 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 5548-55: (6*5)+(5*5)+(4*4)+(3*8)+(2*5)+(1*5)=110 110 % 10 = 0 So 5548-55-0 is a valid CAS Registry Number.