The CAS Registry Mumber 900-15-2 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 9,0 and 0 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 900-15: (5*9)+(4*0)+(3*0)+(2*1)+(1*5)=52 52 % 10 = 2 So 900-15-2 is a valid CAS Registry Number.