The CAS Registry Mumber 99548-20-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,5,4 and 8 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 99548-20: (7*9)+(6*9)+(5*5)+(4*4)+(3*8)+(2*2)+(1*0)=186 186 % 10 = 6 So 99548-20-6 is a valid CAS Registry Number.