RRB Group D · Bite-size lessons
Elementary Statistics
About 6 min · Mathematics · English
Time worked out from the lesson's 344 words at 150 words a minute, plus a minute for each question.
Questions test your ability to calculate central tendencies (mean, median, mode), measure data spread (range), and interpret simple tables, bar charts or pie charts. Focus on arithmetic computation and logical reasoning from given data.
Key ideas
- Mean (Arithmetic Average): Sum of all observations divided by the number of observations. Represents the "central" or typical value. Sensitive to extreme values (outliers). Formula: Mean = (Sum of all values) / (Number of values).
- Median: The middle value when data is arranged in ascending or descending order. For odd number of observations, it's the middle term; for even number, it's the average of the two middle terms. Not affected by extreme values, making it robust for skewed data.
- Mode: The observation that appears most frequently in a dataset. A dataset can have no mode (all values appear once), one mode (unimodal) or multiple modes (bimodal, trimodal). Useful for categorical data like most popular shirt size or most common exam score.
- Range: Difference between the largest and smallest observations in the dataset. Measures the spread or dispersion. Range = Maximum value − Minimum value. A larger range indicates greater variability.
- Data Interpretation: Reading tables, bar graphs, pie charts or line graphs to extract values and perform calculations. Often combined with percentage, ratio or comparison operations. Always check units, scales and legends carefully.
Quick reference
- Mean = Sum ÷ Count. Use for overall average; affected by outliers.
- Median = Middle value after sorting. Robust to extreme values.
- Mode = Most common value. Can have multiple modes or none.
- Range = Max − Min. Measures spread of data.
- Weighted Mean = (Sum of value×weight) ÷ (Sum of weights). Use when observations have different importance.
Check yourself: 3 questions
1. The marks obtained by 7 students in a test are: 45, 52, 38, 60, 55, 48, 52. What is the mode of this data?
2. Find the mean of the first 10 natural numbers.
3. The heights (in cm) of 9 students are: 150, 155, 148, 160, 152, 155, 158, 155, 162. Find the median height.
This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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