The CAS Registry Mumber 53380-71-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,3,8 and 0 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 53380-71: (7*5)+(6*3)+(5*3)+(4*8)+(3*0)+(2*7)+(1*1)=115 115 % 10 = 5 So 53380-71-5 is a valid CAS Registry Number.