High yield5 mapped NDA questions
Build the idea
Statistics questions are usually direct but calculation-heavy. Organise values and frequencies in a table, verify total frequency, and distinguish population-style variance from shortcuts based on an assumed mean.
Concept
Statistics summarises data using measures of central tendency (mean, median, mode) and dispersion (variance, standard deviation). The NDA favours direct, formula-based questions, making this a high-scoring topic.
Understand how transformations of data affect these measures.
Key Points & Formulas
- Mean = Σx/n; median = middle value (sorted); mode = most frequent value.
- Variance = Σ(x−x̄)²/n; standard deviation = √variance.
- Adding a constant k to every value: mean shifts by k, SD unchanged.
- Multiplying every value by k: mean and SD both scale by |k|.
Worked Example
Q. Find the variance of 2, 4, 6, 8.
Mean = (2+4+6+8)/4 = 5.
Squared deviations: 9, 1, 1, 9; sum = 20.
Variance = 20/4 = 5.