The CAS Registry Mumber 1900-70-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,9,0 and 0 respectively; the second part has 2 digits, 7 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1900-70: (6*1)+(5*9)+(4*0)+(3*0)+(2*7)+(1*0)=65 65 % 10 = 5 So 1900-70-5 is a valid CAS Registry Number.