The CAS Registry Mumber 73844-88-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,8,4 and 4 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 73844-88: (7*7)+(6*3)+(5*8)+(4*4)+(3*4)+(2*8)+(1*8)=159 159 % 10 = 9 So 73844-88-9 is a valid CAS Registry Number.