The CAS Registry Mumber 78424-40-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,4,2 and 4 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 78424-40: (7*7)+(6*8)+(5*4)+(4*2)+(3*4)+(2*4)+(1*0)=145 145 % 10 = 5 So 78424-40-5 is a valid CAS Registry Number.