CBC Grade 8 Mathematics Revision Notes (2026): Complete Strand-by-Strand Guide

Grade 8 Mathematics is the middle year of junior school, and it is where many learners either settle into the subject or start to quietly fall behind. The topics are not new in name: numbers, algebra, measurement, geometry and data all appeared in Grade 7. What changes is the depth. Grade 8 asks learners to combine skills, work through problems with several steps, and explain their method rather than just write an answer.

These notes walk through the Grade 8 Maths strands one at a time, in plain language, with short worked examples you can try at the kitchen table. Use them as a revision backbone: read a section, try the practice examples, then move to a full paper. Where your child's textbook or teacher uses slightly different topic names, follow the school; the skills underneath are the same.

How Grade 8 Maths is organised

CBC (now CBE) Mathematics in junior school is arranged into strands, and each strand is broken into sub-strands. The table below gives a practical overview of what learners typically meet in Grade 8 and the skill that matters most in each area. Treat it as a revision checklist rather than an official syllabus document.

Strand 1: Numbers

Numbers is the foundation for everything else in the year. A learner who is shaky with negative numbers or fractions will lose marks in algebra and measurement too, even if they understand those topics.

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Integers

The rules learners must know cold: adding a negative is the same as subtracting; subtracting a negative is the same as adding; two negatives multiplied or divided give a positive; one negative gives a negative. A number line drawn in the margin solves most confusion.

Fractions and decimals

To add or subtract fractions, find a common denominator first. To multiply, multiply tops and bottoms. To divide, flip the second fraction and multiply. Always simplify the final answer. When converting a fraction to a decimal, divide the top by the bottom.

Squares and square roots

Learners should know the squares of whole numbers up to at least 15 by heart, because they appear inside area, Pythagoras-style reasoning and square root questions. For larger numbers, finding square roots by factorisation (breaking the number into prime factors and pairing them) is a reliable method that shows working.

Rates, ratio, proportion and percentages

This is the most "real life" part of Grade 8 Maths: sharing money, comparing prices, working out speed, and finding percentage increase or decrease. Questions are usually wordy, so the key skill is reading slowly and writing down what is given before calculating.

Practice example (not an official KNEC item): Share KSh 1,200 between Amina and Brian in the ratio 3:5.

1. Total parts: 3 + 5 = 8.
2. One part: 1,200 ÷ 8 = 150.
3. Amina: 3 × 150 = KSh 450. Brian: 5 × 150 = KSh 750.
4. Check: 450 + 750 = 1,200. Correct.

Strand 2: Algebra

Algebra frightens many Grade 8 learners, but at this level it is mostly about tidy, patient steps.

Algebraic expressions

Learners collect like terms (3a + 5a = 8a, but 3a + 5b stays as it is), expand brackets (2(x + 4) = 2x + 8) and factorise simple expressions by taking out a common factor (6y + 9 = 3(2y + 3)). Substitution questions ask them to replace letters with numbers and work out the value.

Linear equations

The golden rule: whatever you do to one side, do to the other. Write each step on a new line.

Practice example: Solve 4x − 7 = 2x + 9.

1. Subtract 2x from both sides: 2x − 7 = 9.
2. Add 7 to both sides: 2x = 16.
3. Divide both sides by 2: x = 8.
4. Check by substituting: 4(8) − 7 = 25 and 2(8) + 9 = 25. Both sides match.

Linear inequalities

Inequalities work like equations, with one extra rule: if you multiply or divide both sides by a negative number, the inequality sign flips. Learners should also practise showing the answer on a number line, using an open circle for < or > and a closed circle for ≤ or ≥.

Strand 3: Measurement

Measurement questions carry a lot of marks and reward learners who keep a formula card. Most errors here are unit errors, not maths errors.

Circles

Circumference = π × diameter (or 2πr). Area = πr². Learners must read whether the question gives the radius or the diameter, and use the value of π the question tells them to use (often 22/7 or 3.14).

Practice example: Find the area of a circle of radius 7 cm, taking π as 22/7. Area = 22/7 × 7 × 7 = 154 cm². Notice the answer carries square units.

Area, volume and capacity

Area of a triangle is half base times height; area of a trapezium is half the sum of the parallel sides times the height. Volume of a cuboid is length times width times height; volume of a cylinder is πr²h. Remember that 1 litre equals 1,000 cm³, which links volume to capacity.

Time, money and commercial arithmetic

Expect questions on the 24-hour clock, timetables, profit and loss, discount, commission and simple interest. Writing a one-line statement of what each number means ("cost price = 800") before calculating cuts most mistakes.

Strand 4: Geometry

Geometry is the strand where neatness earns marks. A blunt pencil or a wobbly compass can turn a correct method into a wrong answer.

• Angles: angles on a straight line add to 180°, angles at a point add to 360°, and angles in a triangle add to 180°. Learners should name the rule they use.
• Constructions: practise bisecting a line, bisecting an angle, and constructing 60°, 90°, 45° and 30° with ruler and compasses only. Leave construction arcs visible; they are part of the method.
• Coordinates and graphs: plot points carefully (x along, y up), draw straight-line graphs from a table of values, and read values off a graph.
• Scale drawing: convert real distances with the given scale, draw accurately, then measure and convert back.
• Common solids: recognise nets of cubes, cuboids, prisms and pyramids, and count faces, edges and vertices.

Strand 5: Data handling and probability

Data questions look easy, which is exactly why careless marks are lost here. Learners should practise drawing and reading bar graphs, line graphs and pie charts, and calculating the mean (add all values and divide by how many there are), the mode (most common value) and the median (middle value once arranged in order).

Practice example: The marks of five learners are 12, 15, 9, 15 and 14. Mean = 65 ÷ 5 = 13. Mode = 15. Median: arrange as 9, 12, 14, 15, 15, so the median is 14.

For probability, the basic idea is: probability = number of favourable outcomes ÷ total number of outcomes. A probability is always between 0 and 1, which gives learners a quick way to check their answer.

A simple four-week revision plan

Short, regular sessions beat one long weekend cram. Twenty-five minutes a day with a break is enough for most Grade 8 learners. If the week goes wrong, our guide to a revision timetable that survives a bad week shows how to recover without panic.

How parents can help (even if Maths was not your subject)

• Ask your child to explain one worked example to you. Explaining is the fastest way to find gaps.
• Check that every answer has working shown and units where needed.
• Use the marking approach in our guide on how to mark your child's past paper at home, and help them build the habit described in teaching a child to check their own work.
• Make sure they have a working ruler, protractor, compasses and a sharp pencil long before any exam.

For notes in every other learning area this term, see our Grade 8 notes for all subjects, and browse the Grade 8 resources hub. Because Grade 8 work feeds into the Grade 9 assessment, the KJSEA Mathematics sample paper with answers is a useful look at where these topics lead.

Frequently asked questions

Is Grade 8 Maths examined nationally?

The national junior school assessment is KJSEA at the end of Grade 9. Grade 8 work still matters: school-based assessment across junior school contributes to the final outcome, and Grade 9 Maths builds directly on these topics.

Which strand should my child revise first?

Start with Numbers. Fractions, negatives and percentages appear inside almost every other strand, so fixing them first makes the rest of revision easier.

My child gets the method right but the answer wrong. What should we do?

That is good news; the understanding is there. Slow down the arithmetic, write one step per line, and always check by substituting back or estimating. Accuracy improves with practice papers marked carefully.

Are the worked examples here from real exams?

No. They are practice examples written to show the method. Use them to build confidence, then move on to full practice papers.

For a complete set of notes, practice papers and marking schemes in one download, get the Grade 8 All Subjects Bundle, or the Grade 8 Term 3 Complete Bundle for this term's exams.