The CAS Registry Mumber 81053-88-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,0,5 and 3 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 81053-88: (7*8)+(6*1)+(5*0)+(4*5)+(3*3)+(2*8)+(1*8)=115 115 % 10 = 5 So 81053-88-5 is a valid CAS Registry Number.