The CAS Registry Mumber 73844-90-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,8,4 and 4 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 73844-90: (7*7)+(6*3)+(5*8)+(4*4)+(3*4)+(2*9)+(1*0)=153 153 % 10 = 3 So 73844-90-3 is a valid CAS Registry Number.