The CAS Registry Mumber 83398-40-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,3,9 and 8 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 83398-40: (7*8)+(6*3)+(5*3)+(4*9)+(3*8)+(2*4)+(1*0)=157 157 % 10 = 7 So 83398-40-7 is a valid CAS Registry Number.