The CAS Registry Mumber 87689-40-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,6,8 and 9 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 87689-40: (7*8)+(6*7)+(5*6)+(4*8)+(3*9)+(2*4)+(1*0)=195 195 % 10 = 5 So 87689-40-5 is a valid CAS Registry Number.