Grade 6 Primes & Composites Worksheets
Decide whether a number is prime, pick the primes out of a list, and prove a number is not one.
Every sheet below is generated fresh with a matching answer key. Pick one of the three levels, preview it, and print or download the PDF — no account, no watermark. For the other grade 6 factors & multiples skills, see all factors & multiples worksheets.
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Factors & Multiples · Grade 6
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Grade 6 · 3 pages · A4What each level generates
Grade 6 primes & composites — the exact skill behind each difficulty setting, straight from the generator.
- Level 1Prime or composite?
- Level 2Find the primes
- Level 3Show it is not prime
Grade levels follow the progression common to most English-language curricula — not one specific national curriculum. Every level shows exactly what it generates, so you can check the fit with your own program. See the full scope & sequence →
More Grade 6 factors & multiples skills
Each one generates a different kind of question, with its own three levels and answer key.
- Divisibility TestsUse the digit rules to tell what divides a number without dividing it.
- Prime FactorsBreak a number down into the primes it is made of, and build it back up again.
- Common Factors & HCFFind what two or three numbers share, and the largest factor common to them all.
- Common Multiples & LCMFind the numbers two or three counts land on together, and the first one of them.
Frequently asked questions
▸What is the difference between the HCF and the LCM?
The highest common factor is the largest number that divides into both, so it is never bigger than the smaller of the two. The lowest common multiple is the smallest number both divide into, so it is never smaller than the larger of the two. Saying those two boundaries out loud catches most wrong answers before they are written down.
▸Is the HCF the same as the GCF?
Yes. Highest common factor is the British name and greatest common factor the American one, and greatest common divisor or GCD means the same again. CCSS 6.NS.B.4 calls it the greatest common factor; the questions on these sheets say highest common factor throughout, so tell your student the two names are one idea before they meet the other one in a textbook.
▸How do you find the HCF or LCM of three numbers?
Two at a time. Find the answer for the first two numbers, then find it again for that answer and the third number. It works for both, and HCF of three and LCM of three are built for exactly this — it is also the level where multiplying everything together stops giving the right answer, since the lowest common multiple of 3, 4 and 6 is 12 rather than 72.
▸How does this help with fractions?
Directly. The highest common factor is what takes a fraction to lowest terms in one move — 18/24 has an HCF of 6, so it goes straight to 3/4 rather than through 9/12 — and the lowest common multiple of two denominators is the common denominator you need before adding or subtracting them. Both skills are on this page.
▸Are the primes and prime factors sheets the same as the Grade 5 ones?
No — both move up at this grade. Prime or composite? and Find the primes work from 11 to 99 at Grade 5 and from 101 to 199 here, which is the point where a known table stops settling the question and a number like 143 or 187 has to be tried against 7, 11 and 13. Prime Factors runs higher at every level too, reaching 200, 900 and 800 where Grade 5 reaches 100, 400 and 300. Divisibility Tests changes as well, from three-digit numbers at Grade 5 to four-digit numbers here, and the two common-factor and common-multiple sheets are new at this grade.