Final answer:
Michael purchases 5 half-page advertisements and 8 full-page advertisements.
Step-by-step explanation:
Let's define the following variables:
x = number of half-page advertisements
y = number of full-page advertisements
Now, we can create a system of equations:
Equation 1: 40x + 75y = 800 (since the total cost of the advertisements should be $800)
Equation 2: x + y = 13 (since the total number of advertisements should be 13)
To solve this system of equations, we can use the method of substitution or elimination. Let's use the elimination method:
Multiplying Equation 2 by 40, we get:
40x + 40y = 520
Subtracting this equation from Equation 1, we eliminate x:
35y = 280
Dividing both sides by 35, we find y = 8.
Substituting this value back into Equation 2, we can find x:
x + 8 = 13
x = 5.
Therefore, Michael purchases 5 half-page advertisements and 8 full-page advertisements.