The CAS Registry Mumber 5090-50-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,0,9 and 0 respectively; the second part has 2 digits, 5 and 0 respectively. Calculate Digit Verification of CAS Registry Number 5090-50: (6*5)+(5*0)+(4*9)+(3*0)+(2*5)+(1*0)=76 76 % 10 = 6 So 5090-50-6 is a valid CAS Registry Number.