The CAS Registry Mumber 28124-23-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,8,1,2 and 4 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 28124-23: (7*2)+(6*8)+(5*1)+(4*2)+(3*4)+(2*2)+(1*3)=94 94 % 10 = 4 So 28124-23-4 is a valid CAS Registry Number.