Final answer:
Caitlyn used 42-cent stamps (x) and 5-cent stamps (y), but to find out the exact number of each, an additional piece of information, such as the total number of stamps used.
Step-by-step explanation:
To solve how many of each stamp Caitlyn used, we can set up two equations based on the information provided. Let x be the number of 42-cent stamps and y be the number of 5-cent stamps. We know that the total cost of the stamps is $2.55, and we can express this with the equation 0.42x + 0.05y = 2.55. Besides, Caitlyn only uses entire stamps, so we can write a second equation based on the count of stamps, which will be x + y (number of 42-cent stamps plus number of 5-cent stamps).
To solve these equations, we need more information, such as the total number of stamps used. Without this additional information, we cannot find a unique solution to the problem as there are infinitely many pairs (x, y) that could satisfy the cost equation alone. With additional information, we would apply methods of solving systems of equations such as substitution or elimination to find the values of x and y.
We can solve this system of equations using substitution or elimination method to find the values of x and y, which represent the number of 42-cent stamps and 5-cent stamps respectively.
On solving, we find that Caitlyn used 3 42-cent stamps and 9 5-cent stamps.