The CAS Registry Mumber 5242-03-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,2,4 and 2 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 5242-03: (6*5)+(5*2)+(4*4)+(3*2)+(2*0)+(1*3)=65 65 % 10 = 5 So 5242-03-5 is a valid CAS Registry Number.