The CAS Registry Mumber 1767-20-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,7,6 and 7 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1767-20: (6*1)+(5*7)+(4*6)+(3*7)+(2*2)+(1*0)=90 90 % 10 = 0 So 1767-20-0 is a valid CAS Registry Number.