The CAS Registry Mumber 101889-42-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,1,8,8 and 9 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 101889-42: (8*1)+(7*0)+(6*1)+(5*8)+(4*8)+(3*9)+(2*4)+(1*2)=123 123 % 10 = 3 So 101889-42-3 is a valid CAS Registry Number.