The CAS Registry Mumber 88720-42-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,8,7,2 and 0 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 88720-42: (7*8)+(6*8)+(5*7)+(4*2)+(3*0)+(2*4)+(1*2)=157 157 % 10 = 7 So 88720-42-7 is a valid CAS Registry Number.