The CAS Registry Mumber 107680-45-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,7,6,8 and 0 respectively; the second part has 2 digits, 4 and 5 respectively. Calculate Digit Verification of CAS Registry Number 107680-45: (8*1)+(7*0)+(6*7)+(5*6)+(4*8)+(3*0)+(2*4)+(1*5)=125 125 % 10 = 5 So 107680-45-5 is a valid CAS Registry Number.