The CAS Registry Mumber 99875-21-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,8,7 and 5 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 99875-21: (7*9)+(6*9)+(5*8)+(4*7)+(3*5)+(2*2)+(1*1)=205 205 % 10 = 5 So 99875-21-5 is a valid CAS Registry Number.