Worked examples
Two examples
Example 1
Is 51 prime or composite?
- Try the small primes. 2 does not go in. 3 does: 3 × 17 = 51.
- A number with a factor other than 1 and itself is composite.
Answer: Composite
Example 2
Write 60 as a product of primes.
- Divide by the smallest prime that goes in, again and again: 60 = 2 × 30 = 2 × 2 × 15 = 2 × 2 × 3 × 5.
- Every factor is now prime.
Answer: 2 × 2 × 3 × 5
Where this is taught: Quiz 7: Factors, Multiples, and Primes, “Prime factorization: a number’s recipe”
The drill
Ten problems
How many:
For prime or composite, tap your answer. For a product of primes, type every prime, as many times as it is used, like 2 × 2 × 3 (an x or a * between them is fine). Then press Check my answers at the bottom.Write your answer on the line, or circle it. The answer key, with the reasoning, is on the last page.