The CAS Registry Mumber 1153-55-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,1,5 and 3 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 1153-55: (6*1)+(5*1)+(4*5)+(3*3)+(2*5)+(1*5)=55 55 % 10 = 5 So 1153-55-5 is a valid CAS Registry Number.