The CAS Registry Mumber 80304-23-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,3,0 and 4 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 80304-23: (7*8)+(6*0)+(5*3)+(4*0)+(3*4)+(2*2)+(1*3)=90 90 % 10 = 0 So 80304-23-0 is a valid CAS Registry Number.