Trends, Interpolation, and Extrapolation
Read between the points, then beyond them
Three question verbs, one skill
A huge share of Science points comes from three moves. Identify the trend: as X increases, what does Y do? Interpolate: estimate a value between two measured points. Extrapolate: extend the pattern beyond the last measurement. All three start the same way, by stating the pattern in plain words before looking at any answer choice.
Say the trend as a sentence: as pressure rises, volume falls. Direct relationships move together; inverse relationships move oppositely. Some data does neither, peaking in the middle or flattening at the ends, and the ACT loves those shapes precisely because as one increases, the other increases is wrong for them.
Interpolation is reading a value the table skipped. If 20 degrees gives 31 g and 30 degrees gives 39 g, then 25 degrees should give roughly 35 g, assuming the change between points is smooth. The ACT expects the assumption; answer choices are spaced so a rough midpoint estimate lands cleanly on one option.
Extending past the data
Extrapolation extends the pattern past the last point. If each 10-degree step added about 8 g across the whole table, the step from 40 to 50 degrees most likely adds about 8 more. Follow the established rate of change; do not invent a new one. If the steps were shrinking, keep shrinking them.
The safest extrapolation continues the most recent behavior of the data. A curve that rose steeply and then leveled off should be extended nearly flat, not steeply. Match the tail of the data, not its early slope and not your intuition about the phenomenon.
Science remains an optional section on the enhanced ACT, so budget your prep time deliberately. If your programs want it, trend questions are the highest-yield skill in the section. If none of your schools use it, these 40 minutes of test may not be worth adding to your test day at all.
Watch for the phrase varied directly versus varied inversely in answer choices, and translate before judging: directly means same direction, inversely means opposite directions. Then check the actual columns. A single row that breaks the pattern is enough to sink a claim that the relationship held across the entire experiment.
When a question asks which graph best represents the data in a table, sketch the trend arrow in your head first: rising, falling, rising-then-flat, peaked. Then match shapes. Deciding the shape before looking at the four thumbnails keeps the wrong graphs from arguing with you.