The CAS Registry Mumber 80552-91-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,5,5 and 2 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 80552-91: (7*8)+(6*0)+(5*5)+(4*5)+(3*2)+(2*9)+(1*1)=126 126 % 10 = 6 So 80552-91-6 is a valid CAS Registry Number.