A good experiment answers exactly one question at a time. These questions test whether you can spot what an experiment actually proves — and what it does not.
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A fair experiment changes only ONE thing at a time — everything else must stay exactly the same.
📌 Reading an experiment correctly
Independent variable: the ONE thing the scientist deliberately changes.
Dependent variable: the result that is measured, which may change because of it.
Control group: a version with NO change applied, used for comparison — without it, you cannot be sure the change caused the result.
Olympiad trap: if two things are changed at once (say, both temperature AND light), you cannot tell which one caused the result — this is called a poorly controlled experiment, and Achievers questions test exactly this flaw.
A data table hides its story in the numbers — the trick is reading what changes together, and by how much.
📊 Plant growth vs sunlight hours (a sample data set)
| Sunlight (hours/day) | Plant height after 2 weeks (cm) |
|---|---|
| 2 hours | 4 cm |
| 4 hours | 9 cm |
| 6 hours | 14 cm |
| 8 hours | 18 cm |
Reading the trend: as sunlight increases, plant height also increases — a positive relationship. But this data alone does NOT prove sunlight is the ONLY cause; other factors (water, soil) must have been held constant for that conclusion to be valid.
A Venn diagram question asks you to place items where two or more circles overlap, or where they do not.
✨ Worked example
Living things AND things that need water
the overlap
Plants and animals belong in the overlap — both are living and need water.
Things that need water but are NOT alive
outside the "living" circle
A car engine needs water (as coolant) but is not alive.
Pro tip: before placing an item, check EVERY circle it could belong to — the most common error is stopping after finding just one true match and missing that a second circle also applies.
12 NSO-pattern questions on experimental design, graphs and Venn diagrams, including two Achievers-level questions.
