The CAS Registry Mumber 25987-55-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,9,8 and 7 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 25987-55: (7*2)+(6*5)+(5*9)+(4*8)+(3*7)+(2*5)+(1*5)=157 157 % 10 = 7 So 25987-55-7 is a valid CAS Registry Number.