The CAS Registry Mumber 108920-05-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,9,2 and 0 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 108920-05: (8*1)+(7*0)+(6*8)+(5*9)+(4*2)+(3*0)+(2*0)+(1*5)=114 114 % 10 = 4 So 108920-05-4 is a valid CAS Registry Number.