The CAS Registry Mumber 105202-55-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,2,0 and 2 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 105202-55: (8*1)+(7*0)+(6*5)+(5*2)+(4*0)+(3*2)+(2*5)+(1*5)=69 69 % 10 = 9 So 105202-55-9 is a valid CAS Registry Number.