Spot direct and inverse trends in ACT Science data, describe how two variables relate, and interpolate or extrapolate a value beyond the rows the table gives you.
As one variable increases, the other increases (line rises).
Read down the second column as the first column climbs.
As one variable increases, the other decreases (line falls).
A single table can show a direct trend in one column and an inverse trend in another.
A value between two listed inputs gives an output between the two listed outputs.
Safe because the data brackets your estimate on both sides.
Beyond the last row, continue the trend — state direction, not a precise number.
Riskier than interpolation; the ACT usually asks only "greater or less?"
Ask whether a trend is steady, speeding up, slowing down, or reversing.
"Increases" and "increases at a constant rate" are different claims.
Once you can look up a value, the ACT raises the bar: it asks how the numbers move together. Does one variable rise as another rises? Fall as the other rises? Does the pattern hold, or does it reverse partway through? These "trends and relationships" questions are still pure data reading — you never need outside science — but now you read a column or a curve as a whole rather than one cell.
Ninety percent of ACT trend questions come down to one of two patterns:
Read down the table's second column while the first column climbs. If the second column climbs too, the relationship is direct; if it drops, it is inverse. Consider:
| Fertilizer (g per pot) | Plant height (cm) | Time to first flower (days) |
|---|---|---|
| 0 | 12 | 61 |
| 10 | 19 | 54 |
| 20 | 27 | 48 |
| 30 | 33 | 45 |
| 40 | 38 | 43 |
As fertilizer increases, height increases — a direct relationship. As fertilizer increases, time to flower decreases — an inverse relationship. One table, two different relationships, and you name each just by watching which way the column moves.
The ACT often offers four choices that all say "as X increases, Y ___" and differ only in the verb and a reason. Precision wins:
Interpolation means estimating a value between two rows the table actually lists. If the question asks for plant height at g of fertilizer, note that sits halfway between g ( cm) and g ( cm). Halfway between and is about cm. You are not measuring; you are reasoning that a value between two known inputs should give an output between the two known outputs.
Interpolation is safe because the data brackets your answer on both sides. The ACT rewards it heavily — many "which value is most likely" questions are just interpolation in disguise.
Extrapolation means extending a trend past the last row. If fertilizer went to g, height would likely be a bit above cm — the trend is still rising, so the next value continues upward, though by a small amount given the slowing pattern. Extrapolation is riskier than interpolation because nothing beyond the table confirms the trend keeps going, so the ACT usually asks only for the direction ("would the height be greater or less than cm?") rather than a precise number. Follow the established trend and state the direction confidently, but do not invent a exact figure the data cannot support.
Sometimes the correct answer is "no relationship" — one variable changes while the other stays flat or wanders with no pattern. If the second column reads while the first climbs steadily, the honest description is that the first variable has little or no effect. Do not force a trend onto noise; a nearly constant column is itself the finding.
Master these five moves and trend questions become as mechanical as the lookups — you are simply reading the shape of the data instead of a single point in it.
Table 1 shows how the volume of a gas changes as pressure increases at constant temperature.
| Pressure (kPa) | Volume (mL) |
|---|---|
| 50 | 120 |
| 100 | 60 |
| 150 | 40 |
| 200 | 30 |
Based on Table 1, what is the relationship between pressure and volume?
Table 1 records a runner's data at increasing speeds.
| Speed (km/h) | Stride length (m) | Strides per minute |
|---|---|---|
| 8 | 1.2 | 111 |
| 12 | 1.5 | 133 |
| 16 | 1.8 | 148 |
| 20 | 2.0 | 167 |
As speed increases, how do stride length and strides per minute each change?
Table 1 shows a battery's charge time.
| Charging current (A) | Time to full charge (min) |
|---|---|
| 1 | 240 |
| 2 | 120 |
| 4 | 60 |
| 8 | 30 |
Estimate the time to full charge at a charging current of 3 A.
Table 1 shows the height of a ball dropped from a tower.
| Time (s) | Distance fallen (m) |
|---|---|
| 1 | 5 |
| 2 | 20 |
| 3 | 45 |
| 4 | 80 |
Which statement best describes how distance fallen changes with time?
Table 1 shows a metal wire's electrical resistance at increasing temperatures.
| Temperature (°C) | Resistance (ohms) |
|---|---|
| 20 | 5.0 |
| 40 | 5.6 |
| 60 | 6.2 |
| 80 | 6.8 |
If the trend continues, would the resistance at 100 °C most likely be greater than or less than 6.8 ohms?
Table 1 shows an enzyme's reaction rate at different temperatures.
| Temperature (°C) | Reaction rate (units per min) |
|---|---|
| 10 | 8 |
| 20 | 19 |
| 30 | 31 |
| 40 | 33 |
| 50 | 17 |
| 60 | 4 |
Which statement best describes how reaction rate changes as temperature rises from 10 °C to 60 °C?
Naming a relationship from only the first two rows. A column can rise, then fall (or level off), so an early pattern may reverse.
Scan the whole column top to bottom before committing. If it changes direction, describe the peak or valley, not just the opening trend.
Confusing "increases" with "increases at a constant rate." The direction can be steady while the rate speeds up or slows down.
Look at the gaps between consecutive rows. Growing gaps mean an accelerating rise; shrinking gaps mean the increase is slowing.
Extrapolating a precise number far beyond the data, as if the trend is guaranteed to continue exactly.
Beyond the last row, state only the direction (greater or less) unless the choices force an estimate. Nothing past the table confirms the trend holds.
Forcing a trend onto a nearly constant column just because the other variable changes.
If the second column barely moves (e.g., 50, 49, 51, 50), the honest reading is little or no relationship — a flat column is a valid finding, not a trend to invent.
Table 1 shows how the brightness of a bulb changes with the current through it.
| Current (A) | Brightness (lumens) |
|---|---|
| 0.5 | 210 |
| 1.0 | 430 |
| 1.5 | 640 |
| 2.0 | 850 |
Based on Table 1, what is the relationship between current and brightness?
Table 1 shows how a spring's length depends on the mass hung from it.
| Mass (g) | Spring length (cm) |
|---|---|
| 100 | 14 |
| 200 | 18 |
| 300 | 22 |
| 400 | 26 |
Using Table 1, estimate the spring length when a mass of 250 g is hung from it.
Table 1 shows total rainfall collected over time during a storm.
| Time (h) | Total rainfall (mm) |
|---|---|
| 1 | 4 |
| 2 | 10 |
| 3 | 18 |
| 4 | 28 |
Which statement best describes how the total rainfall changed over the four hours?
Table 1 shows the average braking distance of a car at increasing speeds on dry pavement.
| Speed (km/h) | Braking distance (m) |
|---|---|
| 40 | 9 |
| 60 | 20 |
| 80 | 36 |
| 100 | 56 |
If the trend continues, the braking distance at 120 km/h would most likely be:
Table 1 records a plant's growth rate at increasing amounts of a nutrient.
| Nutrient (mg per L) | Growth rate (mm per day) |
|---|---|
| 5 | 3 |
| 10 | 7 |
| 15 | 10 |
| 20 | 10 |
| 25 | 6 |
Which statement best describes the relationship between nutrient amount and growth rate?
Table 1 shows how far a projectile lands from its launch point at different launch angles, with launch speed held constant.
| Launch angle (degrees) | Range (m) |
|---|---|
| 15 | 39 |
| 30 | 68 |
| 45 | 78 |
| 60 | 68 |
| 75 | 39 |
Based on Table 1, which conclusion about launch angle and range is best supported?
How to read values, units, and axes off ACT Science tables and graphs — and how to pull a single fact out of a busy figure without needing any outside science knowledge.
Judge whether ACT Science data actually supports a stated conclusion, tell a supported claim from an overreach, and name the new evidence that would confirm a result.