Label the vertical axis as the amount of charged battery and the horizontal axis as the time.
Practice makes perfect
We want to sketch a graph that represents the given situation. To do so, let's start by drawing the axes. We will label the vertical axis as the amount of charged battery and the horizontal axis as the time. Alternatively, the reverse order can be done.
The initial point will be the initial percentage of battery charge. This point will have a vertical value but its horizontal value will be equal to zero, because it represents the initial time. Now, let's analyze the first part of the situation.
A fully-charged battery loses its charge at a constant rate until it has no charge left.
This represent a decreasing line segment starting at the initial percentage of battery and ending until it touches the horizontal axis.
Now, let's see the next part of the situation.
You plug it in, and it fully recharges at a constant rate.
This means that the charged battery increases until it reaches the initial percentage of battery. We can draw it as a increasing line segment starting from the end point of the first segment and ending at the initial percentage of battery.
After that we have the next situation.
Then it loses its charge at a constant rate until it has no charge left.
Again, this will be a decreasing line ending until touches the horizontal axis.
