The CAS Registry Mumber 78385-66-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,3,8 and 5 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 78385-66: (7*7)+(6*8)+(5*3)+(4*8)+(3*5)+(2*6)+(1*6)=177 177 % 10 = 7 So 78385-66-7 is a valid CAS Registry Number.