When you have a value, put it back in the original sentence or equation. If it does not fit, you solved the wrong thing. Four choices make this cheap: try the one you picked, not all four unless you are stuck. Rereading the target is in reread the last sentence.
Check the question they asked
x = 5 can be right while the item asked for x + 2. Area, a percent, or the other variable are the usual last-sentence swaps. Formulas worth checking against are in ACT Math formulas.
Two-pass timing is in the two-pass method. Desmos can graph the original equation as a second check, in Desmos on the ACT.
The bottom line
Substitute. If the original statement is false, keep working.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.