The CAS Registry Mumber 98911-42-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,8,9,1 and 1 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 98911-42: (7*9)+(6*8)+(5*9)+(4*1)+(3*1)+(2*4)+(1*2)=173 173 % 10 = 3 So 98911-42-3 is a valid CAS Registry Number.