The CAS Registry Mumber 7305-72-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,3,0 and 5 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 7305-72: (6*7)+(5*3)+(4*0)+(3*5)+(2*7)+(1*2)=88 88 % 10 = 8 So 7305-72-8 is a valid CAS Registry Number.