Data Interpretation and Statistics
What you must understand
Candidates must read tables, bar charts, line graphs, and pie charts accurately, and compute the mean, median, mode, and range. Know how to find a missing value given the mean, and how to interpret trends and comparisons. For pie charts, remember that each sector's angle is proportional to its share of the total (360° for the whole).
Traps to watch for
- Mean vs median: an outlier pulls the mean but barely affects the median. Questions often ask which is more representative.
- Finding a missing total: if the mean of five values is 12, the total is 60; subtract the known values to find the missing one.
- Median with even counts: average the two middle values after sorting.
- Axis scales: a graph whose vertical axis does not start at zero can exaggerate small differences.
- Pie chart totals: convert angles to counts by multiplying the fraction of 360° by the total, not by the raw angle.
Worked example
The mean of four numbers is 15. Three of them are 10, 18, and 14. Find the fourth. Total = 4 × 15 = 60. Sum of known values = 10 + 18 + 14 = 42. Fourth number = 60 − 42 = 18.
Rule of thumb: mean × count = total. This single relationship solves most missing-value questions.