The CAS Registry Mumber 84200-42-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,4,2,0 and 0 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 84200-42: (7*8)+(6*4)+(5*2)+(4*0)+(3*0)+(2*4)+(1*2)=100 100 % 10 = 0 So 84200-42-0 is a valid CAS Registry Number.