The CAS Registry Mumber 54387-10-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,4,3,8 and 7 respectively; the second part has 2 digits, 1 and 0 respectively. Calculate Digit Verification of CAS Registry Number 54387-10: (7*5)+(6*4)+(5*3)+(4*8)+(3*7)+(2*1)+(1*0)=129 129 % 10 = 9 So 54387-10-9 is a valid CAS Registry Number.