Primary 5 Maths: Decimals

Updated Sept 2026

P5 decimal skills: multiplying and dividing decimals by 10, 100, 1000 and by whole numbers, converting between measures, and rounding decimals — worked examples with common mistakes.

Most schools typically cover this topic in Term 1, around weeks 5–8 — though every school sets its own sequence.

Primary 5 decimals is really about place value in motion. Once a child can multiply or divide a decimal by 10, 100 or 1000 without a calculator, three other skills follow directly from the same idea: multiplying and dividing decimals by whole numbers, converting between measurement units (which are almost always powers of 10 apart), and rounding a decimal to a sensible number of places. MOE's 2021 Primary Mathematics Syllabus sets this out as Primary 5 scope, working with decimals up to 3 decimal places.

The rule underneath every question here: multiplying by 10 moves every digit one place more significant — the decimal point effectively shifts one place to the right; dividing by 10 shifts it one place to the left. Multiplying or dividing by 100 shifts two places, and by 1000 shifts three places. The digits themselves never change — only where the decimal point sits relative to them.

P5 Decimals: the mistakes to watch for

• Moving the decimal point the wrong way. Multiplying makes a number larger, so the point moves right; dividing makes a number smaller, so the point moves left. When in doubt, estimate first: 3.2 ÷ 100 must be smaller than 3.2, so 32 is wrong and 0.032 is right.
• Losing track of place value when converting units. "1.5 km = 150 m" is a common wrong answer — 1 km = 1000 m, so the conversion is ×1000, not ×100. Write out the conversion fact (1 km = 1000 m) before multiplying.
• Rounding by just chopping off digits. Rounding 5.847 to 1 decimal place means looking at the digit after the one being kept (the 4) to decide whether to round up — chopping straight to 5.8 without checking would coincidentally work here, but only checking the next digit makes the method reliable every time.
• Forgetting the units on the final answer. A working of "364 ÷ 10 = 36.4" is worthless to a marker without "cm" or "m" attached — decimal questions are almost always about a measurement, not a bare number.

P5 Decimals: shifting the decimal point

P5 Decimals: multiplying and dividing by 10, 100 and 1000

P5 Decimals: exam-style conversions and rounding

PSLE challenge: multi-step decimal and conversion problems

How to practise this topic

Drill the ×10/×100/×1000 shifts until they're automatic — every conversion and every rounding question in this topic is that same shift wearing a different costume. A quick estimate before calculating ("this should end up smaller than 3.2") catches almost every decimal-point slip before it becomes a wrong answer. Decimals also underpin the arithmetic in P5 Volume, where the cm³-to-litre conversion is exactly this ×1000 / ÷1000 skill applied to a tank of water, and the same working style carries into P5 Word Problems.

What this topic covers

In the MOE Primary Mathematics syllabus, Primary 5 Decimals includes the concepts below. (P5-M-03 is Test Paper's own topic code, not an MOE reference.)

• Decimals up to 3 decimal places
• Addition of decimals
• Subtraction of decimals
• Multiplication of decimals
• Division of decimals
• Rounding decimals
• Converting between fractions and decimals
• Decimal word problems

Before this topic

These topics feed into Decimals — if this one wobbles, check them first: Primary 4 Decimals · Primary 4 Multiplication & Division.

Where to go next

• Other Primary 5 topics: Primary 5 Fractions · Primary 5 Percentage · Primary 5 Area & Perimeter
• All Primary 5 Maths topics, or every P4–P6 topic
• Not sure this is the weak topic? How to find which Maths topics your child is weak in