The CAS Registry Mumber 109977-82-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,9,9,7 and 7 respectively; the second part has 2 digits, 8 and 2 respectively. Calculate Digit Verification of CAS Registry Number 109977-82: (8*1)+(7*0)+(6*9)+(5*9)+(4*7)+(3*7)+(2*8)+(1*2)=174 174 % 10 = 4 So 109977-82-4 is a valid CAS Registry Number.