The CAS Registry Mumber 93561-90-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,3,5,6 and 1 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 93561-90: (7*9)+(6*3)+(5*5)+(4*6)+(3*1)+(2*9)+(1*0)=151 151 % 10 = 1 So 93561-90-1 is a valid CAS Registry Number.