Finding All Factor Pairs of Numbers to 50
About this lesson
Partners use an organized list to find every pair of whole numbers that multiplies to make a given number up to 50. They practise multiplication facts and learn a system for knowing when they have found every pair. You need only the board, scrap paper and pencils, and it takes about 12 minutes.
- Grade
- 4
- Subject
- Math
- Time
- 12 min
- Prep
- 2 min
Objective
Students will find all factor pairs for a whole number up to 50 by using an organized list.
Prep
2 min: write the numbers 12, 18, 24, 30, 36 and 48 on the board
Materials
- whiteboard and marker
- scrap paper
- pencils
Steps
- Write 12 on the board and ask which two whole numbers multiply to make 12, recording 1 × 12, 2 × 6 and 3 × 4 in order. Show that 4 × 3 repeats a pair, so you can stop there.
- Have partners choose one number from the board and list all of its factor pairs on scrap paper. They test 1, then 2, then 3, and keep going in order.
- When a pair finishes, they swap papers with another pair to check for missing or incorrect pairs, then choose a new number.
- In the last 3 minutes, call on pairs to share the factor pairs for each number while you build a class chart. Ask which number had the most factor pairs and how they knew they had found them all.
Quick Check
Each student writes all the factor pairs of 20 on scrap paper and hands it in. Look for 1 × 20, 2 × 10 and 4 × 5.
Differentiation
Make it easier: Use numbers under 20 and let students draw rectangular arrays or use counters to test each pair.
Make it harder: Challenge pairs to find the number under 50 with the most factor pairs and to name three numbers that have only one factor pair.
Good For
- Morning warm-up
- Review
- Supply teacher
- Early finishers
