Last reviewed: 25 October 2026
Data handling is often seen as an easy topic, yet many learners drop marks through small slips, such as forgetting to order numbers before finding the median or misreading a graph’s scale. This guide covers the averages, the main charts and the checks that stop those slips. Data handling and probability is a full strand in KICD’s Grade 9 Mathematics curriculum design.
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Collecting and Organising Data
Raw data is a list of values, such as the marks of 20 learners. A tally table and a frequency table organise it: each value is listed with how many times it occurs. Always check that the frequencies add up to the total number of items. If 20 learners were surveyed, the frequency column must total 20.
The Mode
The mode is the value that appears most often. In 4, 7, 7, 9, 10, 7, 3 the mode is 7. A set can have two modes, or none if every value appears once. In a frequency table, the mode is the value with the highest frequency, not the frequency itself. This is one of the most common mistakes.
The Median
The median is the middle value when the data is arranged in order. For 3, 4, 7, 7, 7, 9, 10 the median is 7, the fourth of seven values. With an even number of values, take the two middle numbers and find their average: for 2, 5, 8, 11 the median is (5 + 8) ÷ 2 = 6.5. Always order the data first.
The Mean
The mean is the total divided by the number of values. For 4, 7, 7, 9, 10, 7, 3 the total is 47 and there are 7 values, so the mean is about 6.7. From a frequency table, multiply each value by its frequency, add these products, and divide by the total frequency.
Example: goals scored in 10 matches: 0 goals (2 matches), 1 goal (3), 2 goals (4), 3 goals (1). Total goals = 0 + 3 + 8 + 3 = 14. Mean = 14 ÷ 10 = 1.4 goals per match.
Working backwards is common too. If the mean of five numbers is 12, their total is 60. If four of them add up to 47, the fifth is 13.
The Range
The range is the highest value minus the lowest. For marks from 34 to 89 the range is 55. It shows how spread out the data is, which helps when comparing two classes with similar means.
Bar Graphs
Bar graphs compare categories. Read the scale carefully: if each grid line stands for 5 learners, a bar halfway between 20 and 25 represents roughly 22 or 23 learners, so read as precisely as the scale allows. Bars should have equal widths and equal gaps, and both axes need labels.
Pie Charts
A pie chart shows how a whole is divided. The full circle is 360°. To find each angle, divide the item’s value by the total and multiply by 360. If 12 of 40 learners walk to school, their sector is 12/40 × 360 = 108°. To read a pie chart, reverse the process: a 90° sector is a quarter of the total.
Line Graphs
Line graphs show change over time, such as rainfall per month or temperature during a day. Look at where the line rises fastest, where it falls and where it is level. Questions may ask for the difference between two points, so read both carefully from the scale.
Which Average to Use
The mean uses every value but can be pulled by one extreme value. The median is better when there are outliers, such as one very high salary. The mode suits categories, such as the most popular shoe size in a shop.
Practice and Next Steps
Collect real data at home, such as daily temperatures or family heights, then calculate the averages and draw a chart. The exam countdown has five free questions a day, and the What to Revise report tells you which topics still need work. See the Grade 9 Maths topics list and the Grade 7 Mathematics papers. Full timed papers with worked answers come with the Monthly Pass (KSh 500 by M-Pesa).