The CAS Registry Mumber 78999-54-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,9,9 and 9 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 78999-54: (7*7)+(6*8)+(5*9)+(4*9)+(3*9)+(2*5)+(1*4)=219 219 % 10 = 9 So 78999-54-9 is a valid CAS Registry Number.