The CAS Registry Mumber 91972-78-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,9,7 and 2 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 91972-78: (7*9)+(6*1)+(5*9)+(4*7)+(3*2)+(2*7)+(1*8)=170 170 % 10 = 0 So 91972-78-0 is a valid CAS Registry Number.