The CAS Registry Mumber 39507-99-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,9,5,0 and 7 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 39507-99: (7*3)+(6*9)+(5*5)+(4*0)+(3*7)+(2*9)+(1*9)=148 148 % 10 = 8 So 39507-99-8 is a valid CAS Registry Number.