The CAS Registry Mumber 87840-53-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,8,4 and 0 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 87840-53: (7*8)+(6*7)+(5*8)+(4*4)+(3*0)+(2*5)+(1*3)=167 167 % 10 = 7 So 87840-53-7 is a valid CAS Registry Number.