The CAS Registry Mumber 11121-90-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,1,1,2 and 1 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 11121-90: (7*1)+(6*1)+(5*1)+(4*2)+(3*1)+(2*9)+(1*0)=47 47 % 10 = 7 So 11121-90-7 is a valid CAS Registry Number.