The CAS Registry Mumber 15502-55-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,5,5,0 and 2 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 15502-55: (7*1)+(6*5)+(5*5)+(4*0)+(3*2)+(2*5)+(1*5)=83 83 % 10 = 3 So 15502-55-3 is a valid CAS Registry Number.