Let's denote Ashley's original average as
x
x. After her average decreased by 12 points, her new average became
x
−
12
x−12. After completing the extra credit assignment, her final average increased by 5 points, resulting in a final average of
(
x
−
12
)
+
5
(x−12)+5.
The equation representing this situation is:
(
x
−
12
)
+
5
=
78
(x−12)+5=78
This equation states that Ashley's final average, after the decrease and increase, is equal to 78. Now, you can solve this equation to find the original average,
x
x.
