The CAS Registry Mumber 3947-55-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,9,4 and 7 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 3947-55: (6*3)+(5*9)+(4*4)+(3*7)+(2*5)+(1*5)=115 115 % 10 = 5 So 3947-55-5 is a valid CAS Registry Number.