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Prime factorization
Telling prime numbers from composite ones up to 100, and writing a number as a product of primes.
The PDF has this sheet, its answer key and a guide for grown-ups.
How to help
Split the number into any two factors, then split each again until every factor is prime. Write them smallest first and check by multiplying.
prime a number with exactly two factors: 1 and itself composite a number with more than two factors factor a number that divides evenly into another prime factorization a number written as primes multiplied Watch for: Calling 1 prime (it has only one factor). Stopping at a composite factor: 60 = 4 × 3 × 5. Calling 51 or 91 prime because they're odd.
At home: Pick a number like 36 and draw a factor tree together. Try a different first split and see that the primes come out the same.
Sample sheet and answer key
Luna's Space Adventure
Grade 5 · Prime factorization · 5.NS.2
Name Date
Astronaut Luna is exploring a far-off corner of space. Solve each problem to help Luna's mission go smoothly!
29 prime composite
78 prime composite
99 prime composite
13 prime composite
89 prime composite
44 prime composite
36 = × × × 12 = × × 50 = × × 100 = × × × 60 = × × × 78 = × ×
2 × 2 × 5 × 13 = 2 × 11 × 13 = 2 × 2 × 5 × 7 = 2 × 2 × 3 × 13 = 2 × 2 × 5 × 11 = 3 × 5 × 11 =
36 2 × 2 × 3 × 3 4 × 3 × 3 2 × 2 × 3 × 2
90 2 × 3 × 3 × 5 6 × 3 × 5 2 × 3 × 3 × 2
Grade 5 · Sheet Luna's Space Adventure
Grade 5 · Prime factorization · 5.NS.2
Answer key Astronaut Luna is exploring a far-off corner of space. Solve each problem to help Luna's mission go smoothly!
29 prime composite
78 prime composite
99 prime composite
13 prime composite
89 prime composite
44 prime composite
36 = 2 × 2 × 3 × 3 12 = 2 × 2 × 3 50 = 2 × 5 × 5 100 = 2 × 2 × 5 × 5 60 = 2 × 2 × 3 × 5 78 = 2 × 3 × 13
2 × 2 × 5 × 13 = 260 2 × 11 × 13 = 286 2 × 2 × 5 × 7 = 140 2 × 2 × 3 × 13 = 156 2 × 2 × 5 × 11 = 220 3 × 5 × 11 = 165
36 2 × 2 × 3 × 3 4 × 3 × 3 2 × 2 × 3 × 2
90 2 × 3 × 3 × 5 6 × 3 × 5 2 × 3 × 3 × 2
Answer key Something wrong with this sheet? A wrong answer, a hard-to-read picture? Report it
New problems every time, three levels (gentle, core and stretch), themes to pick from, a second page if you want one. Each sheet comes with an answer key and a one-page guide for grown-ups.
Standard
Virginia SOL 5.NS.2 · Tell prime from composite numbers up to 100 and find a number's prime factorization.
Also: Texas TEKS 5.4A
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