This mini-lesson walks you through the whole KS3 Number strand: place value, ordering, primes, factors & multiples, HCF & LCM, the four operations, order of operations, powers, roots & standard form, fractions ↔ decimals ↔ percentages, and rounding & estimation.
Work through each screen, answer the questions as you go (some are calculations, some are true/false ideas) and collect ⭐ stars. Press Start when you're ready.
A digit's value depends on its column. Reading left to right, each column is worth ten times the one to its right — and to the right of the decimal point the columns get ten times smaller.
Watch out: the 0 in 306 is a place-holder — it keeps the 3 in the hundreds column. Drop it and 306 becomes 36, a totally different number.
To order numbers, compare them column by column, starting from the left. We write comparisons with inequality symbols:
Watch out with decimals: more digits does not mean bigger! 0.7 is greater than 0.65, because 7 tenths beats 6 tenths — compare the tenths column first.
Negatives: the further left on the number line, the smaller. So -5 < -2 (−5 is colder / lower than −2).
Tap the greater number in each pair. Compare column by column!
Watch out: 1 is not prime (it has only one factor). 2 is the only even prime — every other even number is divisible by 2.
Tap a number, then tap the box it belongs in.
Every whole number can be written as a product of primes. A factor tree breaks it down step by step until every branch ends on a prime:
Tip: circle each prime as you reach it so you don't forget it. The order you split doesn't matter — you always get the same primes.
The HCF is the biggest number that divides into both. The LCM is the smallest number that is a multiple of both. A Venn diagram of prime factors makes it easy:
12 = 2 × 2 × 3 18 = 2 × 3 × 3
HCF = product of the shared primes = 2 × 3 = 6
LCM = every prime, using the most it appears = 2 × 2 × 3 × 3 = 36
Add, subtract, multiply and divide work with integers, decimals and fractions. The trickiest part at KS3 is negative numbers:
When a calculation has several operations, do them in this order:
3 + 4 × 2² → do the index first: 2² = 4
3 + 4 × 4 → then multiply: 4 × 4 = 16
3 + 16 = 19 (not 3+4=7, then ×… that would be wrong!)
Watch out: reading strictly left to right gives the wrong answer. 3 + 4 × 2 = 11, not 14, because you multiply before you add.
A power (or index) tells you how many times to multiply a number by itself. A root undoes a power — they are inverse operations.
Watch out: 5² is not 5 × 2 = 10. The little 2 means "multiply by itself", so 5 × 5 = 25.
Standard form writes a number as A × 10ⁿ, where A is between 1 and 10. It's a neat way to handle very big or very small numbers.
Watch out: the first part must be at least 1 but under 10. So 32 × 10² is not standard form — it should be written 3.2 × 10³.
Fractions, decimals and percentages are the same idea written differently. You should be able to swap between them:
Terminating decimals (like 0.5, 0.75, 0.2) stop after a few digits and always come from a simple fraction: 0.75 = ¾, 0.2 = ⅕.
"Percent" means "out of 100". To find a percentage of an amount, turn it into a fraction or decimal and multiply:
10% of £45 = £45 ÷ 10 = £4.50
20% = double 10% = £9.00
(Or: 0.2 × 45 = £9.00.)
Handy building blocks: 50% = ÷2, 25% = ÷4, 10% = ÷10, 1% = ÷100. Build any percentage from these.
To round, look at the next digit: 5 or more rounds up, 4 or less rounds down.
Estimate by rounding every number to 1 significant figure first: 19 × 31 ≈ 20 × 30 = 600.
Error bounds: a length given as 12 cm to the nearest cm could really be anywhere from 11.5 cm up to 12.5 cm — half a unit either side.
Place value: a digit's worth depends on its column.
Ordering: compare left to right; < and > point at the smaller number.
Primes/factors: HCF = shared primes, LCM = all primes (most of each).
BIDMAS: Brackets, Indices, ÷×, +−.
Powers & roots: inverse operations; 5² = 25, √25 = 5.
Standard form: A × 10ⁿ with 1 ≤ A < 10.
FDP: ½ = 0.5 = 50%; percentages are just operators.
Rounding: 5-or-more rounds up; estimate with 1 s.f.
You've covered the whole KS3 Number strand. Press Finish to see your score.
You've worked through Number for KS3 Mathematics. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.