This domain is all about ratios, rates, percentages, proportions, and statistics — the "real-world math" questions. They're wordy, so careful reading beats clever tricks.
Percent translation: "of" → multiply, "is" → equals, "what" → the variable. "15 is 20% of what?" becomes 15 = 0.20 × n.
The essentials
- Percent change = (new − old) / old × 100. Always divide by the original.
- Discount: a 25% discount means you pay 75%. Final = 0.75 × original.
- Rate = quantity ÷ time. Set up a proportion for "at that rate" questions.
- Mean = sum ÷ count → so sum = mean × count. This rearrangement unlocks most average questions.
- Median = middle value when ordered; resistant to outliers, unlike the mean.
Two-step percent trap: A price up 20% then down 20% is NOT back to start — it's 0.80 × 1.20 = 0.96, a 4% net drop. Percentages don't cancel.