The CAS Registry Mumber 75305-83-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,3,0 and 5 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 75305-83: (7*7)+(6*5)+(5*3)+(4*0)+(3*5)+(2*8)+(1*3)=128 128 % 10 = 8 So 75305-83-8 is a valid CAS Registry Number.