Answer: There is 11% chance that the next costumer will buy a blank card.
Explanation:
Since we have given that
Number of thank you cards = 167
Number of birthday cards = 285
Number of blank cards = 56
So, Total number of cards is given by
167+285+56=508
So, Probability that the next costumer will buy a blank card is given by

Hence, there is 11% chance that the next costumer will buy a blank card.