Primary 6 · Number & Algebra

P6 algebra

In P6, a letter stands for a number. Your child writes algebraic expressions from words, simplifies them, evaluates them by substitution and solves simple equations, all linear with no brackets.

Taught in
Term 2
Syllabus
4 skills
Usual slip
Multiplying instead of adding

n + 3 and 3n drawn as bars

What your child learns in P6 algebra

Four skills, each with what it looks like on a worksheet.

Follows the latest (2026) MOE syllabus
See the syllabus wording
  • using a letter to represent an unknown number
  • notation, representations and interpretation of simple algebraic expressions such as a ± 3, a × 3 or 3a, a ÷ 3 or a/3
  • simplifying simple linear expressions excluding brackets
  • evaluating simple linear expressions by substitution
  • simple linear equations involving whole number coefficient only

A letter for a number

The letter stands for a number not known yet. n + 3 is 3 more than n, 3n means 3 × n, and n ÷ 3 can be written n/3. The boxes show terms, not sizes.

n + 3 and 3n

Simplifying

Add or take away like terms only. 5k + 2k + 6 = 7k + 6. The 6 has no k, so it stays apart. The boxes show terms, not sizes.

5k + 2k + 6 = 7k + 6

Substituting a value

Put the number in place of the letter. If n = 8, then 3n = 3 × 8 = 24, never 38, and n + 3 = 11.

n3nn + 3
82411
When n = 8

Simple equations

Find the number that makes both sides equal. 2n + 5 = 17, so 2n = 12 and n = 6. Check it: 2 × 6 + 5 = 17. The boxes show terms, not sizes.

2n + 5 = 17

Key facts and formulas

Term 2
  • A letter stands for an unknown number3a=3×a,a3=a÷33a = 3 \times a, \quad \frac{a}{3} = a \div 3
  • Solve 2x + 5 = 17: undo each step, then check2x → 17−5=17 - 5 = 1212x → 12÷2=12 \div 2 = 66check → 2×6+5=2 \times 6 + 5 = 1717
  • Add or take away like terms only5a+2−2a+4=3a+65a + 2 - 2a + 4 = 3a + 6
  • Substitute a = 4 into 3a + 63×4+6=3 \times 4 + 6 = 1818

Words to know

Letter
A number that is not known yet, such as n.
Expression
Numbers and letters joined by operations, such as 3n + 2.
Like terms
Terms with the same letter, such as 5k and 2k. Only these combine.
Substitute
Put a number in place of the letter.
Equation
Two sides that are equal, such as 2n + 5 = 17.

The sentence that costs the mark

A blue ribbon is n cm long. A red ribbon is 3 cm longer than the blue one. Write the length of the red ribbon, in terms of n.

What the working usually does

3 timesn=3n

Puts the 3 and the n together into 3n. But 3n means 3 × n, three whole ribbons, not one ribbon a little longer.

What the question asked

3 more thann=n + 3

One ribbon with 3 cm added on the end. Longer adds, so the 3 sits beside the n with a plus.

Both are real algebra, and 3n is the tidier answer. If the blue ribbon were 10 cm, the red one is 13 cm, not 30. That is the check that settles it.

The same P6 algebra question, worked properly

Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.

Crate J is xx kg, Crate K is 3x3x kg, and Crate L is 2 kg heavier than K. When x=6x = 6, find the total mass of the crates.

Step 1 of 5▌
  1. x is a number of kilograms. Crate J is x kg, and Crate K is 3x kg, where 3x means 3 × x.
  2. Crate L is 2 kg heavier than Crate K, so add 2: Crate L is 3x + 2 kg. Heavier does not mean 2 times.
  3. Add the three crates: x + 3x + 3x + 2 = 7x + 2. The 2 has no x, so it stays apart.
  4. Substitute x = 6, so the total mass is 7 × 6 + 2 = 44 kg.
  5. So the three crates have a combined mass of 44 kg.

Every question in StudyLah comes with a walkthrough like this one.

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Two quick P6 algebra questions

Try them together, then tap to check.

Question 1

Priya and Raj had 180 stamps in total. Priya had pp stamps and Raj had 40 more than her. Find the number of stamps Raj had.

Show answer

Answer110. Raj has p + 40, so p + p + 40 = 180. Then 2p = 140, p = 70, and Raj has 70 + 40 = 110.

Question 2

Find the value of 5y−7+3y25y − 7 + \frac{3y}{2} when y=4y = 4.

Show answer

Answer19. 5y is 5 × 4 = 20 and the fraction is 3 × 4 ÷ 2 = 6, so 20 − 7 + 6 = 19.

Helping at home

How to tell it has clicked

When your child writes an expression from a sentence, ask them to read it back in words, then read the question aloud too.

"Three times n" and "three more than n" sound different said out loud. Reading 3n back as "three more than n" is the exact gap.

Try this tonight

Pick a number for n at dinner, say 6. Ask for 3 more than it, then 3 times it. Nine and eighteen, from two different words.

Then write them: n + 3 and 3n. Same two symbols, two different meanings.

Before and after P6 algebra

  1. Builds on

    Primary 5 Whole Numbers and Four Operations

    Does the operations in the right order

  2. You are here

    Primary 6 Algebra

    Uses a letter for an unknown number

The methods your child will use here

More in Primary 6

Struggling with the working rather than the topic itself? How to help your child with problem sums

See how your child is doing on this topic

StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.

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