The CAS Registry Mumber 42761-33-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,2,7,6 and 1 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 42761-33: (7*4)+(6*2)+(5*7)+(4*6)+(3*1)+(2*3)+(1*3)=111 111 % 10 = 1 So 42761-33-1 is a valid CAS Registry Number.