The CAS Registry Mumber 82507-91-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,2,5,0 and 7 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 82507-91: (7*8)+(6*2)+(5*5)+(4*0)+(3*7)+(2*9)+(1*1)=133 133 % 10 = 3 So 82507-91-3 is a valid CAS Registry Number.