The CAS Registry Mumber 74785-83-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,7,8 and 5 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 74785-83: (7*7)+(6*4)+(5*7)+(4*8)+(3*5)+(2*8)+(1*3)=174 174 % 10 = 4 So 74785-83-4 is a valid CAS Registry Number.