The CAS Registry Mumber 5240-43-7 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 0 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 5240-43: (6*5)+(5*2)+(4*4)+(3*0)+(2*4)+(1*3)=67 67 % 10 = 7 So 5240-43-7 is a valid CAS Registry Number.