The CAS Registry Mumber 74320-28-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,3,2 and 0 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 74320-28: (7*7)+(6*4)+(5*3)+(4*2)+(3*0)+(2*2)+(1*8)=108 108 % 10 = 8 So 74320-28-8 is a valid CAS Registry Number.