Data Representation

Data Representation questions on the ACT Science section test your ability to read and interpret information presented in graphs, tables, scatter plots, and charts. These questions make up about 30-40% of the Science section and are generally the most straightforward question type.

What You Need to Know

Data Representation passages present scientific data in visual formats. You will NOT need to know the science behind the data — you only need to read and interpret the information that is given to you. Every answer can be found directly in the data or by identifying patterns within it.

Key Skills

How to Approach Data Representation Questions

1. Read the title and labels first. Before looking at the data itself, understand what is being measured and what the axes or columns represent.
2. Scan the data for patterns. Spend 10-15 seconds identifying the overall trend: is the data going up, down, or fluctuating?
3. Go to the question. Read what is being asked, then return to the specific part of the data that answers it.
4. Eliminate wrong answers. If the data shows an increasing trend, any answer suggesting a decrease is wrong.

Step-by-step example:
A table shows plant growth (cm) at different light levels (hours/day):
4 hrs → 2.1 cm | 8 hrs → 4.5 cm | 12 hrs → 6.8 cm | 16 hrs → 7.0 cm

Question: "What is the relationship between light exposure and plant growth?"
Answer: As light exposure increases, plant growth increases, but the rate of increase slows at higher light levels (from 4→8 hrs the growth nearly doubles, but from 12→16 hrs it barely changes).

Common Data Formats

Graph Reading Skills

When reading values from a graph, be precise:

• Use a straightedge: Mentally (or physically) draw a line from the data point to both axes to read exact values.
• Watch the scale: Axes may not start at zero. A graph starting at 50 can make a change from 52 to 54 look enormous.
• Multiple lines: When a graph has multiple lines, make sure you are reading the correct one. Check the legend.
• Inverse relationships: When one variable increases and the other decreases, the relationship is inverse (negative correlation).
• Non-linear patterns: Not all data forms straight lines. Look for curves that level off (plateaus), exponential growth, or dips and peaks.
• Outliers: A single data point far from the trend does not change the overall pattern. Do not let one outlier mislead you.

Worked Example: Reading a Multi-Line Graph

Imagine a graph showing dissolved oxygen (mg/L) vs. water temperature (°C) for two lakes:

Lake A: 0°C → 14.6 | 10°C → 11.3 | 20°C → 9.1 | 30°C → 7.6 | 40°C → 6.4
Lake B: 0°C → 12.8 | 10°C → 10.1 | 20°C → 8.2 | 30°C → 6.9 | 40°C → 5.8

Question: "At what temperature do both lakes have approximately the same dissolved oxygen?"
Step 1: Scan for where the values are closest. At 30°C, Lake A = 7.6 and Lake B = 6.9 (difference = 0.7). At 40°C, Lake A = 6.4 and Lake B = 5.8 (difference = 0.6). The values converge as temperature rises.
Step 2: The answer is that both lakes approach similar dissolved oxygen levels at higher temperatures (around 40°C+), where the gap narrows to 0.6 mg/L.

Worked Example: Table with Multiple Variables

A table shows test results for 4 metals heated in air:

Iron: Mass before = 5.00g, Mass after = 5.37g, Color change = silver to orange-brown
Copper: Mass before = 5.00g, Mass after = 5.10g, Color change = orange to black
Magnesium: Mass before = 5.00g, Mass after = 8.29g, Color change = silver to white
Gold: Mass before = 5.00g, Mass after = 5.00g, Color change = none

Question: "Which metal reacted most with oxygen in the air?"
Step 1: The mass increase tells you how much oxygen combined with the metal. Calculate each gain: Iron +0.37g, Copper +0.10g, Magnesium +3.29g, Gold +0.00g.
Step 2: Magnesium had the greatest mass increase, so it reacted most with oxygen.

Worked Example: Extrapolation

A graph shows bacteria population over time:
Hour 0 → 100 | Hour 1 → 200 | Hour 2 → 400 | Hour 3 → 800

Question: "Based on the trend, approximately how many bacteria would be present at Hour 5?"
Step 1: Identify the pattern — the population doubles every hour.
Step 2: Hour 4 → 1,600; Hour 5 → 3,200. The answer is approximately 3,200.
Key insight: This is exponential growth (doubling), not linear growth (adding the same amount each time). The ACT tests whether you can tell the difference.

Common Mistakes

Practice Walkthrough

Here is a mini ACT-style question with a sample dataset.

Passage: Students measured the pH of rainwater samples collected over 5 days in two cities:
City X: Day 1 = 5.8, Day 2 = 5.6, Day 3 = 5.4, Day 4 = 5.3, Day 5 = 5.1
City Y: Day 1 = 6.2, Day 2 = 6.1, Day 3 = 6.0, Day 4 = 6.0, Day 5 = 5.9

Question: Based on the data, which statement is best supported?
A) City X has more acidic rain than City Y on all days measured.
B) City Y's rain will eventually become as acidic as City X's.
C) The pH of rainwater is unrelated to location.
D) City X's rain is becoming less acidic over time.

Solution:
Step 1: Lower pH = more acidic. City X ranges 5.1-5.8; City Y ranges 5.9-6.2. City X is always lower (more acidic). This supports A.
Step 2: Option B makes a prediction not supported by the data (City Y's pH is dropping slowly but there is no evidence it will reach City X's levels). Option C is directly contradicted — location clearly matters. Option D is wrong — City X's pH is decreasing (becoming MORE acidic, not less).
Answer: A

Quick Reference: Data Representation Approach

ACT-Specific Hacks

• No outside knowledge needed: Everything you need is in the passage and data. If an answer requires science knowledge not in the passage, it is wrong.
• Interpolation: Find the two closest data points and estimate proportionally between them.
• Confirm trends: Check at least three data points to confirm a pattern is consistent.
• Watch units: A question might ask for grams when the table shows kilograms.
• Do these first: Data Representation questions are usually the fastest to answer, so tackle them first to bank time for harder passages.
• Labels before data: Always read titles, axis labels, and column headers before looking at actual numbers.
• Speed target: Aim for about 5 minutes per Data Representation passage (including all questions).
• Process of elimination is king: Even if you cannot find the exact answer, eliminating 2-3 wrong choices dramatically improves your odds.
• Graphs that look dramatic may not be: A steep-looking line on a truncated axis (starting at 95 instead of 0) may represent a tiny actual change. Always check the scale.
• When in doubt, go back to the data: The ACT never asks you to guess. If you feel uncertain, the answer is somewhere in the graph or table — re-read it carefully.