Prime and Composite Numbers Worksheets: {FREE} Activity Pack - Free Printable

To solve this problem, we need to decide whether each number is prime or composite.

Let’s go step by step:

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Step 1: Understand the definitions

- A prime number is a whole number greater than 1 that has exactly two factors: 1 and itself.
- A composite number is a whole number greater than 1 that has more than two factors (so it can be divided evenly by numbers other than 1 and itself).

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Step 2: Check each number

✔ 79
Let’s test if 79 is divisible by any number from 2 up to √79 (about 8.9). So check 2, 3, 5, 7.

- Not divisible by 2 (it’s odd)
- 7+9=16 → not divisible by 3
- Doesn’t end in 0 or 5 → not divisible by 5
- 79 ÷ 7 ≈ 11.28 → not whole

So 79 is prime

✔ 73
Check divisibility up to √73 (~8.5) → check 2, 3, 5, 7

- Odd → not divisible by 2
- 7+3=10 → not divisible by 3
- Doesn’t end in 0/5 → not divisible by 5
- 73 ÷ 7 ≈ 10.4 → not whole

So 73 is prime

✔ 7
Only factors are 1 and 7 → prime

✔ 75
Ends in 5 → divisible by 5 → 75 = 5 × 15 → has more than two factors → composite

✔ 78
Even number → divisible by 2 → 78 = 2 × 39 → composite

✔ 72
Even → divisible by 2 → also divisible by 3, 4, 6, etc. → composite

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All numbers have been checked correctly.

Final Answer:
The numbers 79, 73, and 7 are prime. The numbers 75, 78, and 72 are composite.