The CAS Registry Mumber 42502-56-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,2,5,0 and 2 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 42502-56: (7*4)+(6*2)+(5*5)+(4*0)+(3*2)+(2*5)+(1*6)=87 87 % 10 = 7 So 42502-56-7 is a valid CAS Registry Number.