The CAS Registry Mumber 100642-88-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,6,4 and 2 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 100642-88: (8*1)+(7*0)+(6*0)+(5*6)+(4*4)+(3*2)+(2*8)+(1*8)=84 84 % 10 = 4 So 100642-88-4 is a valid CAS Registry Number.