What This Episode Covers
In Episode 41 of Real GMAT® Problems, we work through sequences questions from the 11th edition of the Official Guide for GMAT® Review — the out-of-print edition we use in this series specifically because there's no overlap with today's edition, so your official practice material stays fresh. We warm up with a classic half-sequence problem, then ramp up to questions that trip up even well-prepared test-takers.
The central theme of this episode is one of the most underappreciated ideas in GMAT® quant preparation: write everything down clearly, and use fractions instead of decimals whenever you can. Those two habits, applied consistently, are responsible for a surprising number of correct answers in our experience — not just on sequences, but across the quant section broadly. We walk through exactly why, using specific examples from the problems in this episode.
Sequences questions tend to feel mechanical — just keep multiplying or dividing and find the right term. But the mistakes we see happen in predictable ways: misreading what the question is actually asking, making small arithmetic errors when working with fractions in decimal form, and losing track of which term is which when the list gets long. This episode is built around preventing those exact problems, with concrete techniques that are easy to build into your practice habits.
Problems Covered
Problem 1 — Warm-Up: Geometric Sequence A sequence starts at 240 and each term is half the preceding term. We need to find the least term greater than one. This problem introduces the core habit loop: write the question's "what are they asking?" in the margin, list every term in order, and work in fractions from the start. The most common wrong answers (options D and E) come from either doing the arithmetic in decimal form or misidentifying which term crosses the threshold.
Problem 2 — Mid-Level: Longer Sequence Analysis A more challenging sequences question that tests whether you can stay organized across more steps. We discuss when to write out every single term versus when to jump ahead — the general rule is that if there are fewer than about 20 terms, list them all. The payoff for doing so is a safety net: if you make a mistake, you can see it on paper rather than discovering it after you've already submitted an answer.
Problem 3 — Harder: Notation and Reasoning The most difficult problem in the set requires some sequence notation and tests your ability to reason carefully about terms relative to one another. We cover a few organizational techniques that help you keep track of term positions without losing your place mid-problem.
Key Takeaways
- Write "what are they asking?" before you solve. The most common mistake on sequences questions is arriving at the right number but answering the wrong question (e.g., listing the first term less than one instead of the last term greater than one). A quick note in the margin prevents this.
- Use fractions, not decimals. Most sequences problems on the GMAT® involve multiplication by simple fractions. Working in fraction form is almost always cleaner and less error-prone than converting to decimals — especially since there's no calculator in the quant section.
- List every term when you can. On sequences with fewer than ~20 terms, just write them all out. It takes 30 seconds and makes it nearly impossible to mix up positions.
- Condition good habits in practice. The mistakes that happen under time pressure on test day are the same ones that happen in practice when you rush. Rehearsing the "write it down" habit now is what makes it automatic later.
- If the answer choices are fractions, work in fractions. When you see fraction answer choices, that's a signal: don't convert to decimals. The problem was designed to be solved with fraction arithmetic.
Related Reading
- Real GMAT® Problems - Ep. 42 - Statistics — more Official Guide problems with systematic strategies
- Real GMAT® Problems - Ep. 40 - Square Roots — the testing approach applied to roots and radicals