Relevant Selection
What it tests: Work out which pieces of information you're given are actually needed to answer the question, and discard the rest.
Approach: Before you touch a single number, restate in your own words exactly what quantity the question wants, and list every constraint in the prose separately from the table — a row that looks best on paper is worthless if it fails a written rule.
- Identify precisely what the question is asking you to calculate.
- Apply every prose constraint first, eliminating any row that fails one, no matter how good its figures look.
- Only then build the calculation from the columns the question actually needs — other columns in the table may be genuine, consistent data that simply plays no part in this comparison.
- Solve using only the rows and columns that survive both tests, and double-check you haven't inverted a ratio.
Common trap: the two best-looking raw numbers in the table both fail a constraint stated only in the prose — one on product type, one on weight — so a solver who compares every row on value alone, without applying the written rules first, lands on the wrong answer even with correct arithmetic.
"Active nutrient content" is the proportion of the bag's weight that is usable plant nutrient (the rest is bulking material).
| Brand | Type | Bag weight (kg) | Active nutrient content | Price | Coverage area (m²) | Shelf life (months) |
|---|---|---|---|---|---|---|
| GreenGro | Slow-release | 20 | 15% | £15 | 40 | 24 |
| EarthBoost | Quick-release | 20 | 22% | £20 | 45 | 18 |
| TomatoFeed | Slow-release | 18 | 22% | £20 | 42 | 24 |
| RootMax | Slow-release | 24 | 20% | £20 | 50 | 36 |
| BloomRich | Slow-release | 16 | 15% | £16 | 35 | 12 |
| PetalPlus | Slow-release | 14 | 14% | £10 | 30 | 24 |
Nasrin will buy just one bag this season. Tomato plants need a slow-release feed — a quick-release feed would scorch their roots. Her garden shed has one shelf for storing an opened bag, and it cannot hold anything heavier than 20 kg. Using the table, which bag gives her the most active nutrient (in kg) per pound spent, among those that meet BOTH of her requirements?
Reveal the correct answer & explanation
Correct answer: B
First scope the table down using the two prose constraints: EarthBoost is quick-release (unsuitable for tomatoes), and RootMax weighs 24kg (over the shed's 20kg limit) — both must be eliminated before any value comparison, regardless of how good their figures look. For the remaining candidates, build the compound ratio: active nutrient (kg) = bag weight × content %, then divide by price. GreenGro scores 3.0 ÷ 15 = 0.200 kg per £, beating TomatoFeed's 3.96 ÷ 20 = 0.198 kg per £ by about 1%, and clearly beating BloomRich's 0.150 kg per £. Coverage area and shelf life are genuine, consistent data but play no part in this comparison.
Option C (EarthBoost) and D (RootMax) each have a higher raw ratio than GreenGro, but each breaks a different rule stated in the prose — type, then weight — so both must be discarded before ranking. Option E (TomatoFeed) is a genuinely valid, correctly computed candidate, but a close second rather than the winner. Option A (BloomRich) comes from inverting the ratio (treating a higher £-per-kg figure as "better value"), which actually gives the worst ratio among the qualifying bags.


