Answer: a) and b)
 
Step-by-step explanation: Lets find the percentages for each option. 
 
a). with 1-11 without 12-20 
 
Here there are 20 shopers. From 1 to 11, there are 11 shoppers. From 12 to 20, there are 9 shoppers. 11 of 20 have credit cards, and 11/20 = 0.55. So this option is correct 
 
b). with 1-33 without 34-60 
 
Here there are 60 shoppers. 1 to 33 there are 33 shoppers with store credit cards. 33/60 = 0.55. So this is also a simulation which represents this situation. 
 
c). with 1-24 without 25-40 
 
Here there are 40 shoppers. 1 to 24, so there are 24 shoppers with the store credit card. 24/40 = 0.6. So this is not a correct option. 
 
d). with 1-21 without 22-40 
 
Here there are 40 shoppers, of which 21 have the credit card. 21/40 = 0.525, so this is not one of the options 
 
e). with 1-18 without 19-40 
 
Here there are 40 shoppers, of which 18 have the credit card. 18/40 = 0.45, so this is not one of the options. 
 
f). with 1-36 without 37-80 
 
Here there are 80 shoppers, of which 36 have the credit card. 36/80 = 0.45,
so this is not one of the options.