ACT sequence questions ask for the next term or the nth term in an arithmetic sequence (add a constant) or geometric sequence (multiply by a constant)—spot the pattern before you memorize a formula. They are a small but quick-win topic on Math.
Arithmetic sequences
Each term differs by a fixed amount d. Example: 3, 7, 11, 15… → d = 4, next term 19. nth term: aₙ = a₁ + (n-1)d. Listed among topics in ACT Math topics.
Geometric sequences
Each term is multiplied by ratio r. Example: 2, 6, 18, 54… → r = 3. nth term: aₙ = a₁ · r^(n-1).
How to solve fast
- Write the difference or ratio between consecutive terms.
- If differences are constant → arithmetic; if ratios → geometric.
- For "which term equals X," build forward or use the formula.
Do not overcomplicate
Many ACT items need only two or three steps. If a sequence looks like a quadratic second difference pattern, the test usually stops at linear or geometric. Pair with rate problems when growth is described in words.
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.
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