The CAS Registry Mumber 80999-53-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,9,9 and 9 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 80999-53: (7*8)+(6*0)+(5*9)+(4*9)+(3*9)+(2*5)+(1*3)=177 177 % 10 = 7 So 80999-53-7 is a valid CAS Registry Number.