Prime or Composite
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Prime or Composite
Prime or composite worksheet: sixteen numbers to 100 to circle as prime or composite, including odd composites such as 51 and 91 that look prime. Grades 4 and 5 with an answer key.
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Teach it first
Prime and Composite NumbersA teaching handout to hand out before this sheet: the rule, worked examples and common mistakes.- Pages
- 1
- Last updated
- Time
- About 15 minutes
- Answer key
- Included
- Printing
- Black and white
- Related curriculum
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List every factor pair of a number up to 100, tell whether a number is a multiple of another, sort numbers into primes and composites, and find the greatest common factor and the least common multiple.
Reviewed by Mrs. Catherine Reynolds, Teacher. How we check worksheets
How to use this sheet
- Have the child find factors in pairs, starting at 1, and stop when the pairs start to repeat.
- Keep a multiplication chart on hand for the first sheets, then take it away.
- For multiples, have the child skip count aloud and write the first few in a row.
Common mistakes
- Mixing up factors and multiples. Factors of 12 are 12 or smaller; multiples of 12 are 12 or larger.
- Missing 1 and the number itself as factors. Always start the pair list with 1 and the number.
- Calling 1 a prime number. A prime has exactly two factors; 1 has only one.
- Calling every odd number prime. 9, 15 and 21 are odd but composite.
