The CAS Registry Mumber 1325-91-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,3,2 and 5 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1325-91: (6*1)+(5*3)+(4*2)+(3*5)+(2*9)+(1*1)=63 63 % 10 = 3 So 1325-91-3 is a valid CAS Registry Number.