The CAS Registry Mumber 549505-78-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 5,4,9,5,0 and 5 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 549505-78: (8*5)+(7*4)+(6*9)+(5*5)+(4*0)+(3*5)+(2*7)+(1*8)=184 184 % 10 = 4 So 549505-78-4 is a valid CAS Registry Number.