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

Grade 8 Mathematics under Kenya's CBC (now CBE) is where the foundation either locks in — or doesn't. The content covered this year directly feeds into Grade 9 KJSEA performance because so many Grade 9 topics build on Grade 8 concepts. If your child is going to struggle in KJSEA Maths, the gap almost always traces back to something skipped in Grade 8.

This guide walks through every strand in the KICD Grade 8 Maths curriculum design with plain-English explanations and worked examples. Use it as the backbone of holiday revision.

The 5 strands of Grade 8 Mathematics

1. Numbers — integers, fractions, decimals, percentages, ratios, rates, indices
2. Algebra — algebraic expressions, linear equations, simultaneous equations, inequalities
3. Measurement — length, area, volume, capacity, mass, time, money
4. Geometry — angles, polygons, Pythagoras theorem, transformation, coordinates
5. Statistics & Probability — data collection, tables, charts, mean/mode/median, basic probability

Strand 1: Numbers — what Grade 8 must master

Integers and operations

Grade 8 expects fluency with positive and negative integers, including BODMAS (Brackets, Of, Division, Multiplication, Addition, Subtraction) on mixed expressions.

Worked example: Evaluate -5 + (-3) × 4 - (-2)

Apply BODMAS — multiplication first: (-3) × 4 = -12

Now: -5 + (-12) - (-2) = -5 - 12 + 2 = -15

Fractions with different denominators

The operation every Grade 8 learner must not fail: adding/subtracting fractions with different denominators.

Rule: Find the LCM of the denominators. Convert each fraction. Add/subtract the numerators. Simplify.

Worked: 2/3 + 3/4 = ?

LCM(3,4) = 12. So 2/3 = 8/12, 3/4 = 9/12. Sum: 8/12 + 9/12 = 17/12 = 1 5/12.

Percentages — the two must-master moves

1. Find a percentage of a number: 25% of 240 = (25/100) × 240 = 60
2. Express one number as a percentage of another: 30 as a % of 120 = (30/120) × 100 = 25%

Kenyan context problem: a matatu driver buys fuel at KSH 5,000 and fare collections for the day were KSH 6,500. What percentage profit did he make? Profit = 1,500. (1,500/5,000) × 100 = 30%

Ratios and rates

Sharing in a ratio: Mama Wanjiku shares KSH 2,400 between her two children in the ratio 3:5. How much does each receive?

Total parts = 3+5 = 8. One part = 2,400/8 = 300. First child gets 3×300 = KSH 900, second gets 5×300 = KSH 1,500. Check: 900 + 1,500 = 2,400. ✓

Strand 2: Algebra

Solving a linear equation (single variable)

The cardinal rule: whatever you do to one side, do to the other.

Worked: Solve 3x + 7 = 22

1. Subtract 7 from both sides: 3x = 15
2. Divide both sides by 3: x = 5
3. Check: 3(5) + 7 = 15 + 7 = 22 ✓

Simultaneous equations — elimination method

Worked: Solve 2x + y = 11 and x + y = 7.

Subtract the second equation from the first: (2x - x) + (y - y) = 11 - 7 → x = 4.

Substitute back into x + y = 7: 4 + y = 7, so y = 3.

Check in original equation: 2(4) + 3 = 11 ✓.

Inequalities — the one thing that trips learners up

Rule: treat inequalities like equations, EXCEPT when you multiply or divide by a negative number — flip the inequality sign.

Example: Solve -2x + 3 > 7

1. Subtract 3: -2x > 4
2. Divide by -2 AND flip: x < -2

Strand 3: Measurement

Area of a triangle

Area = ½ × base × height. Always squared units.

Triangle with base 10 cm and perpendicular height 6 cm: ½ × 10 × 6 = 30 cm².

Volume of a cuboid

V = length × width × height. Always cubic units.

Cuboid 5 × 4 × 3 cm: V = 60 cm³.

Volume of a cylinder

V = π × r² × h. Square the RADIUS, not the height. This is the single most-missed distinction in Grade 8 Volume.

Cylinder r = 7 cm, h = 10 cm: V = π × 49 × 10 ≈ 1,540 cm³.

Strand 4: Geometry

Pythagoras Theorem

In any right-angled triangle: a² + b² = c², where c is the hypotenuse (longest side, opposite the right angle).

Worked: A right triangle has legs 3 cm and 4 cm. Find the hypotenuse.

3² + 4² = 9 + 16 = 25. So c = √25 = 5 cm. (The classic 3-4-5 triangle — memorise it.)

Angle sum of a polygon

Sum of interior angles = (n - 2) × 180°, where n is the number of sides.

• Triangle (3 sides): (3-2) × 180 = 180°
• Quadrilateral (4 sides): (4-2) × 180 = 360°
• Pentagon (5 sides): (5-2) × 180 = 540°
• Hexagon (6 sides): (6-2) × 180 = 720°

Coordinates and transformation

Points plotted on a Cartesian plane as (x, y). Transformations include:

• Translation — sliding without rotating (every point moves by the same vector)
• Reflection — mirror image across an axis or line
• Rotation — turning by an angle around a centre point

Example: Reflect (3, 2) in the x-axis. The y-coordinate flips sign: (3, -2).

Strand 5: Statistics & Probability

Mean, Mode, Median

Given the data set: 5, 7, 8, 8, 10, 12, 15 — find mean, mode, median.

• Mean = sum / count = (5+7+8+8+10+12+15)/7 = 65/7 ≈ 9.3
• Mode = most frequent = 8
• Median = middle value when sorted = 4th value = 8

Basic probability

P(event) = favourable outcomes / total outcomes

A standard die. Probability of rolling a number greater than 4: favourable = {5, 6} = 2. Total = 6. P = 2/6 = 1/3.

The 2-week revision plan

Don't try to cover everything in one weekend. Over 14 days:

Where to get the full materials

This article is the map. The actual territory — all the practice questions, worked answers, end-of-term exams, and the full strand-by-strand written notes — sits in the paid Grade 8 Mathematics collection at cbcedukenya.com/shop.

• Grade 8 Mathematics — Full Revision Pack — KSH 40
• Grade 8 Mathematics — Complete Notes — KSH 100
• Grade 8 Mathematics — Exam + Marking Scheme — KSH 100
• FREE Grade 8 Sample Pack — no payment required

Pay via M-Pesa Till 5310731, instant download. Or start with the free sample to see the quality before buying.

The honest bottom line

Grade 8 Maths is where competence becomes confidence — or where confusion becomes fear. The strands above are not a complete list of everything that could appear in a test, but they are the backbone. Master these and your learner is ready for Grade 9 KJSEA Maths. Skip them and you're hoping Grade 9 teachers can plug the gaps — they usually can't, because they're teaching Grade 9 content.

Work through one strand at a time. Check understanding by asking your learner to teach it back to you. If they can't explain it, they don't own it. Go again.

Aligned with: KICD Grade 8 Mathematics Curriculum Design, CBC (now CBE) framework. All worked examples use Kenyan contexts (KSH, matatu fares, Wanjiku-shares) where appropriate. For official KICD guidance visit the Ministry Guidelines.