A graph question tests whether you can use numbers to support a claim about a changing effect. Read the claim first and ask what must change as the conditions change. Then read the title, axes, and key so you know what each line measures. Subtract the groups’ values at each level, then compare the gaps to test the claimed change. A choice can report the numbers correctly and still miss what the claim says.
Hints
- Hint 1
Look at the technician’s argument about the inhibitor’s effect. What would you compare to measure protection at one humidity level?
- Hint 2
At each of the three humidity levels, subtract coated rust coverage from uncoated rust coverage. How do those three differences compare?
Step-by-step
Track the coating’s benefit
Step 1Find what measures protection
The argument’s words becomes more pronounced as humidity increases call for evidence of a growing benefit. How do we measure the inhibitor’s protective effect? At the same humidity, subtract coated rust coverage from uncoated rust coverage. That difference measures how much rust the coating prevents, so we’ll track it across humidity levels.
- Step 2
Match the lines to the plates
The graph’s title and vertical axis show the percentage of each plate’s surface covered by rust after seven days. Humidity runs along the horizontal axis, and the key marks coated plates with a solid line and uncoated plates with a dashed line. Compare the lines at the same humidity.
- Step 3
Calculate how the gap changes
How does the gap change? Percentage points measure the difference between percentages, so at 30% humidity the gap is 10 minus 8, or 2 points. At 60%, it’s 35 minus 15, or 20 points; at 90%, it’s 70 minus 25, or 45 points. The gap grows from 2 to 20 to 45 points, which means protection becomes more pronounced as humidity increases.
- Step 4
Connect the contrast to the argument
Which sentence shows that growing benefit? The contrast between nearly the same rust coverage at 30% humidity and much higher rust coverage on uncoated plates at 90% gives a small benefit followed by a large benefit. That contrast supports the technician’s argument. Choice A.