The CAS Registry Mumber 52838-55-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,2,8,3 and 8 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 52838-55: (7*5)+(6*2)+(5*8)+(4*3)+(3*8)+(2*5)+(1*5)=138 138 % 10 = 8 So 52838-55-8 is a valid CAS Registry Number.