ACT Science — quick math on data: percent change, ratios, scaling and unit conversions

ACT's description of the Interpretation of Data category, the largest part of the Science section, includes reasoning mathematically with the data in tables and graphs. In practice that means small calculations done fast and without a calculator, which ACT does not permit in the science section: a percent change between two measurements, how many times larger one value is than another, what happens to an amount when a solution is scaled up, or a speed in different units. None of it is hard, but each has a standard trap, and the wrong options are built from exactly those traps.

This material gives you twelve short data situations, two of them with a drawn bar graph. You find a percent increase and a percent decrease and learn why dividing by the new value instead of the original is the most common error. You separate percentage points from percent when a germination rate goes from 20 to 30 percent. You compute a ratio instead of a difference, scale the salt in a solution up to a full liter, and handle an inverse relationship in which a gas's pressure rises as its volume shrinks. You find a growth rate from two data points and project it forward without counting the starting height as growth. You convert a flow in milliliters per minute into liters over two hours, a speed in kilometers per hour into meters per second, and an area in square centimeters into square meters, where the conversion factor must be squared. Finally you estimate a ratio from a bar graph by rounding to friendly numbers, and find a filling time from a rate.

Every explanation shows the arithmetic in one or two lines and then says which mistake produces each wrong option, so that you learn to recognize the trap as well as to avoid it. The numbers are chosen for mental arithmetic, as they are on the test.

The flashcards collect the rules to have ready: percent change and its trap, percentage points, ratios, scaling, inverse proportion, rates from two points, kilometers per hour to meters per second, square meters to square centimeters, and time from a rate.

This material offers a quiz and flashcards. It is independent practice based on ACT's public description of the ACT Science section; the data are original, and nothing here is produced or endorsed by ACT.

• Compute percent increase and decrease from the original value and distinguish percentage points from percent
• Find ratios between measurements and scale quantities in direct and inverse proportion
• Find a rate from two data points and project it forward correctly
• Convert volume, time, speed and area units without a calculator
• Estimate from a graph by rounding to friendly numbers

Practice material written by Zestly, based on ACT's published description of the ACT Science section (reporting categories Interpretation of Data, Scientific Investigation, and Evaluating Scientific Arguments and Models with Evidence; act.org, retrieved September 2026). All data sets, figures and questions are original.