How do you answer a question that requires reading two figures together, while keeping the units straight?
Combining figures on ACT Science: linking a value from one figure to another through a shared variable, and reading units and scales carefully to avoid factor-of-ten and unit-mismatch errors.
A focused answer on multi-figure ACT Science questions: using a shared variable to carry a value from one figure into another, and reading units, scales, and axis breaks carefully to avoid the factor-of-ten and unit-mismatch errors the test sets up.
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What this topic is asking
Some ACT Science questions cannot be answered from a single figure. Instead, they ask you to link two figures (or a figure and a table) through a shared variable, carrying a value from one to the other. At the same time, the test sets little units and scale traps: a figure labelled in milligrams while the answers are in grams, or a y-axis that jumps in fifties. This page is about doing both reliably: bridging figures and reading units carefully.
Bridging two figures with a shared variable
Multi-figure questions are built on a variable that appears in both figures. The method:
- Identify the shared variable (the axis or column the two figures have in common).
- In the figure that the question gives you a starting value for, read across to find the shared variable's value.
- Take that shared value into the other figure and read off the quantity the question asks for.
For example, if Figure 1 plots pressure against temperature and Figure 2 plots volume against temperature, then temperature is the bridge: a volume from Figure 2 tells you a temperature, and that temperature tells you a pressure from Figure 1.
Reading units, scales, and axis breaks
The second half of this skill is not being fooled by the axis. Three things to check on every figure:
- Units. Read the unit in each axis label or column header. A value of "200" means nothing until you know it is 200 mg/L, 200 g, or 200 percent.
- Scale spacing. Gridlines may be spaced by 1, 2, 5, 10, or 50. Count the spacing before reading between lines, or you will misjudge a value badly.
- Axis breaks and non-zero starts. An axis that starts at 90 instead of 0, or has a zig-zag break, exaggerates small differences. A bar that looks "twice as tall" may represent a tiny real difference.
Translating between a table and a graph
A related task is matching a table to the graph that represents the same data, or vice versa. Check that the trend in the table (rising, falling, flat) matches the shape of the graph, and that a few specific points line up (the value at the start, the peak, the end). This is the data-translation skill the ACT lists explicitly, developed further in translating between graphs and text.
Try this
Q1. Figure A plots solubility against temperature; Figure B plots crystal size against temperature. How would you find the crystal size that corresponds to a given solubility? [2 points]
- Cue. Temperature is the shared variable: use Figure A to find the temperature for the given solubility, then read the crystal size at that temperature from Figure B.
Q2. A graph's y-axis is in grams and an answer choice is in milligrams. A point reads 0.5 g. What is that in milligrams, and why does the unit check matter? [2 points]
- Cue. 0.5 g is mg; matching the figure's unit to the answer's unit avoids a factor-of-1000 error.
Exam-style practice questions
Practice questions written in the style of ACT exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
ACT Science (style)1 marksFigure 1 shows pressure (atm) versus temperature (degrees Celsius); Figure 2 shows volume (L) versus the same temperature. At 50 degrees Celsius, Figure 1 reads 2 atm and Figure 2 reads 4 L. What is the pressure when the volume is 4 L? (A) 1 atm (B) 2 atm (C) 4 atm (D) Cannot be determinedShow worked answer →
A 1-point two-figure question linked by a shared variable.
The correct answer is (B), 2 atm. Temperature is the shared variable. Figure 2 says volume is 4 L at 50 degrees, and Figure 1 says the pressure at 50 degrees is 2 atm, so the pressure when volume is 4 L is 2 atm. (A) and (C) misread a figure, and (D) is wrong because the shared temperature links the two figures. The method is to use the common variable as a bridge.
ACT Science (style)1 marksA graph's y-axis is labelled 'Concentration (mg/L)' with gridlines every 50 units; a question's answer choices are in g/L. A point sits at 200 mg/L. In g/L this is: (A) 0.2 g/L (B) 2 g/L (C) 20 g/L (D) 200 g/LShow worked answer →
A 1-point unit-conversion check, a classic ACT trap.
The correct answer is (A), 0.2 g/L. Since 1 g = 1000 mg, 200 mg/L is g/L. (D) ignores the conversion, and (B) and (C) use the wrong factor. The ACT often labels a figure in one unit and the answers in another, so always match the figure's units to the answer's units before choosing.
Related dot points
- Reading line graphs on ACT Science: locating the axes and units, finding a value at a given point, and naming a trend (direct, inverse, or no relationship) between two variables.
A focused answer on reading line graphs in ACT Science: checking the axes and units first, reading a value at a given point, and identifying whether two variables show a direct, inverse, or no relationship. The most points on the test come from this single skill.
- Reading tables on ACT Science: orienting to the rows, columns, and units, locating a value at an intersection, and tracking how one variable changes while another is held fixed.
A focused answer on reading data tables in ACT Science: orienting to the rows, columns, headers, and units, finding a value at a row-column intersection, and isolating the effect of one variable by holding others constant across a dense multi-variable table.
- Interpolation and extrapolation on ACT Science: estimating a value between known data points and extending a trend beyond the measured range, while flagging the greater uncertainty of extrapolation.
A focused answer on interpolation and extrapolation in ACT Science: estimating a value between two known data points by following the trend, and predicting a value beyond the measured range by extending it, plus why extrapolation is less certain and how the ACT tests both.
- Translating data on ACT Science: matching a verbal description of a relationship to its graph, pairing a table with the graph that represents it, and converting between data forms by checking shape and key points.
A focused answer on translating data on ACT Science: matching a worded description of a relationship to the correct graph, pairing a table with the graph that represents it, and converting between forms by checking the overall shape and a few key points such as the start, the peak, and the end.
- Interpretation of Data question types on ACT Science: reading a value, identifying a trend, comparing data points, and interpolating or extrapolating, each answered straight from the figure.
A focused answer on the Interpretation of Data question types on ACT Science: reading an exact value, naming a trend, comparing two data points, and interpolating or extrapolating, with the figure-first method for each and why this category carries the most points.
Sources & how we know this
- Description of the ACT Science Test — ACT, Inc. (2025)
- ACT Science Section Test Tips — ACT, Inc. (2025)