The CAS Registry Mumber 101685-87-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,1,6,8 and 5 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 101685-87: (8*1)+(7*0)+(6*1)+(5*6)+(4*8)+(3*5)+(2*8)+(1*7)=114 114 % 10 = 4 So 101685-87-4 is a valid CAS Registry Number.