Logarithms — Strategy & Common Mistakes

Below is a focused strategy guide for Logarithms on the ACT math section. Convert between log and exponential form and apply the basic log laws. The advice here is specific to this topic and to the broader Intermediate Algebra category — the patterns that matter, the mistakes that cost the most points, and the sequence to follow when this question type shows up on test day.

Mindset for this topic

Intermediate Algebra is where the ACT separates 28-scorers from 32-scorers. Quadratics, complex numbers, sequences, logs, and matrices all appear. Recognise the family, apply the right technique, do not panic.

For Logarithms specifically, that mindset translates into one rule: read the prompt twice before you write a single symbol. Most students who miss this question type miss it because they jumped to a calculation before they understood what was being asked. The ACT loves to phrase a Logarithms question in a way that sounds like a different topic — a word problem, a diagram, a function in disguise. Slow on the read, fast on the math.

The four most common mistakes on Logarithms

1. Forgetting i² = −1 when multiplying complex numbers.
2. Using the wrong sequence formula (arithmetic vs. geometric — read whether the difference is constant or the ratio is constant).
3. Mis-applying log rules — log(a + b) is not log a + log b.
4. Computing the discriminant but stopping there; finish the quadratic formula.

If you keep a personal "leak list" (we recommend it on the study tips page), add the one mistake from the list above that you have made most recently. Re-read it before every practice session for two weeks; you will stop making it.

The recommended workflow

Identify the topic family. Recall the matching formula. Substitute. Solve. Check by plugging the answer back into the original.

Run this workflow on every Logarithms question you attempt. The first ten times it will feel slow. By the twentieth question it will be automatic, and your accuracy on this topic will jump by 10–20 points worth of raw score.

Pacing

60–80 seconds per question; longer questions can take 100 seconds. On a ACT that mixes question types, you do not want to be the student who spent 3 minutes on a Logarithms question and ran out of time on questions you would have nailed.

What to do next

Open the main Logarithms topic page and re-attempt the six worked questions with this strategy in mind. If you still miss any, use the Logarithms cheatsheet as a one-page reminder, and revisit our Intermediate Algebra formula sheet until the formulas are automatic.