Prime factorisation
Name: _____________________ Date: __________
Show your thinking with numbers, words, or a drawing.
1. Write 72 as a product of prime factors, smallest first.
2. Write 20 as a product of prime factors, smallest first.
3. Write 126 as a product of prime factors, smallest first.
4. Write 90 as a product of prime factors, smallest first.
5. Write 147 as a product of prime factors, smallest first.
Answer key · Prime factorisation
1. 2 × 2 × 2 × 3 × 3
The circled numbers at the ends of the branches are prime: 2, 2, 2, 3, 3.
Write every circled number, including repeats, from smallest to largest, joined by ×.
72 = 2 × 2 × 2 × 3 × 3
2. 2 × 2 × 5
The circled numbers at the ends of the branches are prime: 2, 2, 5.
Write every circled number, including repeats, from smallest to largest, joined by ×.
20 = 2 × 2 × 5
3. 2 × 3 × 3 × 7
The circled numbers at the ends of the branches are prime: 2, 3, 3, 7.
Write every circled number, including repeats, from smallest to largest, joined by ×.
126 = 2 × 3 × 3 × 7
4. 2 × 3 × 3 × 5
The circled numbers at the ends of the branches are prime: 2, 3, 3, 5.
Write every circled number, including repeats, from smallest to largest, joined by ×.
90 = 2 × 3 × 3 × 5
5. 3 × 7 × 7
The circled numbers at the ends of the branches are prime: 3, 7, 7.
Write every circled number, including repeats, from smallest to largest, joined by ×.
147 = 3 × 7 × 7
Try it together
Choose a question from the printable. Use objects or a drawing to show your thinking, then explain your method to someone at home.