The CAS Registry Mumber 115974-99-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,5,9,7 and 4 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 115974-99: (8*1)+(7*1)+(6*5)+(5*9)+(4*7)+(3*4)+(2*9)+(1*9)=157 157 % 10 = 7 So 115974-99-7 is a valid CAS Registry Number.