The least number of boxes Sharon should buy is 5 boxes.
Step-by-step explanation:
Given,
Number of cards in box = 12
Number of stamps in packages = 20
We will find least common multiple of 12 and 20.
12 = 12,24,36,48,60,.....
20 = 20,40,60,80,....
The LCM of 12 and 20 is 60.
Now,
12 cards = 1 box
60 cards =
60 cards = 5 boxes
The least number of boxes Sharon should buy is 5 boxes.