The CAS Registry Mumber 91540-05-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,5,4 and 0 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 91540-05: (7*9)+(6*1)+(5*5)+(4*4)+(3*0)+(2*0)+(1*5)=115 115 % 10 = 5 So 91540-05-5 is a valid CAS Registry Number.