The CAS Registry Mumber 88420-17-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,8,4,2 and 0 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 88420-17: (7*8)+(6*8)+(5*4)+(4*2)+(3*0)+(2*1)+(1*7)=141 141 % 10 = 1 So 88420-17-1 is a valid CAS Registry Number.