The CAS Registry Mumber 109894-55-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,8,9 and 4 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 109894-55: (8*1)+(7*0)+(6*9)+(5*8)+(4*9)+(3*4)+(2*5)+(1*5)=165 165 % 10 = 5 So 109894-55-5 is a valid CAS Registry Number.