The CAS Registry Mumber 87901-78-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,9,0 and 1 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 87901-78: (7*8)+(6*7)+(5*9)+(4*0)+(3*1)+(2*7)+(1*8)=168 168 % 10 = 8 So 87901-78-8 is a valid CAS Registry Number.