If you need 6th grade GCF and LCM worksheets that you can print right now, this page builds them for you — 20 fresh problems, an answer key underneath, and no account to create first. The current sheet starts with problems like LCM of 21 and 6 and LCM of 12 and 6, and the answers (42 and 12) are printed on the key so marking takes about a minute.
‘New set of problems’ opens the generator in its own tab. There you can change the problem count and turn the answer key on or off. ‘Print or save as PDF’ opens the print dialog — choose Save as PDF in the printer list to keep the file. The sheet fits US Letter and A4, and the answer key prints on its own page.
The greatest common factor is what simplifies a fraction; the lowest common multiple is what gives it a common denominator. Both jobs turn up constantly, which is why this topic is worth being fast at.
Factors and multiples pull in opposite directions: factors divide into a number, multiples are built from it. A question like LCM of 21 and 6 answers 42, and knowing which direction the question is asking is half the battle.
Divisibility rules are worth memorising alongside this — even, digit sum divisible by three, ends in zero or five — because they turn LCM of 12 and 6 from a search into a glance.
Prime factorisation is the general tool: break both numbers down, take the shared primes for the factor and all of them for the multiple.
In US classrooms these 6th grade GCF and LCM worksheets are commonly aligned with the number system strand for grades 5 and 6, though the exact wording varies from state to state.
| # | Problem | Answer | What to check |
|---|---|---|---|
| 1 | LCM of 21 and 6 = | 42 | Watch for: swapping factor and multiple |
| 2 | LCM of 12 and 6 = | 12 | Check: stopping at a common factor rather than the greatest |
| 3 | GCF of 42 and 36 = | 6 | Look at: missing one in a factor list |
| 4 | LCM of 30 and 12 = | 60 | Ask about: multiplying the two numbers for the lcm |
| 5 | LCM of 16 and 24 = | 48 | Watch for: leaving the factorisation incomplete |
| 6 | LCM of 25 and 10 = | 50 | Check: treating a prime as having no factors |
Work LCM of 30 and 12 out loud as a demonstration. It gives 60. Children who hear LCM of 30 and 12 reasoned through once at the start of a session make noticeably fewer errors in the ten minutes that follow.
A good first problem to do together is LCM of 21 and 6, which comes out at 42. Do LCM of 21 and 6 once with the child narrating, then hand over the pencil and start the clock on the other 20 problems.
Keys are produced by the same code that produces the questions, so a mismatch between question and answer is not possible on these sheets.
The answer key is generated with the worksheet, not written by hand, so it always matches the sheet in front of you — LCM of 21 and 6 is listed as 42, LCM of 12 and 6 as 12, and so on down the page.
For a class set, print one sheet, press the new-worksheet button and print again. Each child gets different numbers on the same skill, so nobody can copy the answer to LCM of 21 and 6 from a neighbour.
Portrait orientation is what the sheet is designed for. Landscape works but wastes about a third of the paper, so leave the orientation alone unless you have a reason.
Keep the finished 6th grade GCF and LCM worksheets in date order — the drop in time across ten sheets is the clearest progress report you will get.
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Free printable math worksheets from a working math academy director in Korea. Problems come from our own code, not from a published workbook. Every sheet prints on US Letter or A4 with its answer key. All worksheets · Worksheet generator · Korean site
Last updated: 2026-09-13