A linear relationship changes by the same amount over equal time intervals. If a graph marks two points and asks when it reaches another level, compare the drops: equal drops take equal amounts of time. Read the axis values, not the grid boxes, because the axes may use different scales.
Hints
- Hint 1
A labeled point pairs a time with a battery level. Use the two marked points to find how many percentage points the battery loses and how many hours that takes.
- Hint 2
On a linear graph, equal drops take equal amounts of time. Compare the drop to with the drop between the marked points. If they match, which time gap repeats?
Step-by-step
Match equal drops
Step 1Measure the drop between the marked points
No Desmos needed. The line's equal drops give the time directly. Read the labeled points and . Find the drop in battery level:
Find the time it takes:
- Step 2
Match the drop to the target
From the second point, find the drop needed to reach :
That's the same drop as before. Because the relationship is linear, it takes another hours.
- Step 3
Find the time
The battery is at when , so add the next hours:
The battery reaches after hours. Choice C.