Most GRE Quant word problems don't fail people on the math — the arithmetic and algebra involved is usually well within reach. What actually causes errors is translating dense, deliberately awkward English into the correct equation in the first place.
GRE Quant word problems are often written with intentionally convoluted phrasing — nested conditions, relative comparisons, information given out of the order you'd naturally use it. The math, once correctly set up, is frequently simple. The setup is where the exam is actually testing you.
Phrases like “40% more than,” “half as many as,” or “3 less than twice” each translate to a specific, unambiguous mathematical operation — but under time pressure, it's easy to reverse a relationship (writing x = 0.4y instead of y = 1.4x for “x is 40% more than y”) and get a clean-looking, confidently wrong answer.
A reading-comprehension error in Quant doesn't look like an error — it produces a perfectly reasonable number that simply answers the wrong equation. Unlike an arithmetic slip, which often produces an obviously odd result, a translation error slides through unnoticed because everything downstream of the mistake is executed correctly.
Before doing any arithmetic, write out the relationship in symbolic form explicitly — not in your head, on paper (or the digital scratchpad) — and then re-read the original sentence against your symbolic version to confirm it says what you think it says. This adds seconds but catches the exact error type that's hardest to catch by checking your arithmetic alone.
When reviewing missed Quant questions, separate errors into two buckets: “I set up the wrong equation” versus “I set up the right equation but made a math error.” Most people are surprised how heavily the first bucket dominates once they actually track it — and that tracking is what tells you what to actually drill.