The CAS Registry Mumber 79840-25-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,9,8,4 and 0 respectively; the second part has 2 digits, 2 and 5 respectively. Calculate Digit Verification of CAS Registry Number 79840-25: (7*7)+(6*9)+(5*8)+(4*4)+(3*0)+(2*2)+(1*5)=168 168 % 10 = 8 So 79840-25-8 is a valid CAS Registry Number.