The CAS Registry Mumber 90111-42-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,0,1,1 and 1 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 90111-42: (7*9)+(6*0)+(5*1)+(4*1)+(3*1)+(2*4)+(1*2)=85 85 % 10 = 5 So 90111-42-5 is a valid CAS Registry Number.