The CAS Registry Mumber 125023-42-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,5,0,2 and 3 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 125023-42: (8*1)+(7*2)+(6*5)+(5*0)+(4*2)+(3*3)+(2*4)+(1*2)=79 79 % 10 = 9 So 125023-42-9 is a valid CAS Registry Number.