The CAS Registry Mumber 11099-87-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,1,0,9 and 9 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 11099-87: (7*1)+(6*1)+(5*0)+(4*9)+(3*9)+(2*8)+(1*7)=99 99 % 10 = 9 So 11099-87-9 is a valid CAS Registry Number.