The CAS Registry Mumber 303174-78-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,0,3,1,7 and 4 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 303174-78: (8*3)+(7*0)+(6*3)+(5*1)+(4*7)+(3*4)+(2*7)+(1*8)=109 109 % 10 = 9 So 303174-78-9 is a valid CAS Registry Number.