The CAS Registry Mumber 27780-83-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,7,7,8 and 0 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 27780-83: (7*2)+(6*7)+(5*7)+(4*8)+(3*0)+(2*8)+(1*3)=142 142 % 10 = 2 So 27780-83-2 is a valid CAS Registry Number.