The CAS Registry Mumber 79787-20-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,9,7,8 and 7 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 79787-20: (7*7)+(6*9)+(5*7)+(4*8)+(3*7)+(2*2)+(1*0)=195 195 % 10 = 5 So 79787-20-5 is a valid CAS Registry Number.