The CAS Registry Mumber 7090-90-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,0,9 and 0 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 7090-90: (6*7)+(5*0)+(4*9)+(3*0)+(2*9)+(1*0)=96 96 % 10 = 6 So 7090-90-6 is a valid CAS Registry Number.