Adding three numbers means finding the total when three groups are put together. Young learners can make this easier by choosing two numbers to add first. A helpful strategy is to look for an easy pair, such as two numbers that make 10.
This matters because it helps students add faster and with fewer counting mistakes.
Counters are a great way to see how the strategy works. If red counters, blue counters, and green counters show three numbers, students can move them to make a friendly pair first. For example, 7 + 3 + 4 becomes 10 + 4, which is easy to solve as 14.
The total stays the same even when the groups are rearranged.
Key Facts
- To add three numbers, choose two numbers to add first, then add the third.
- Making 10 is a helpful strategy: 7 + 3 + 4 = 10 + 4 = 14.
- The order of addition can change, but the sum stays the same: 2 + 5 + 8 = 8 + 2 + 5.
- The grouping can change, but the sum stays the same: (6 + 4) + 3 = 6 + (4 + 3).
- Look for pairs that make 10: 1 + 9, 2 + 8, 3 + 7, 4 + 6, 5 + 5.
- Add two then the third: a + b + c = (a + b) + c.
Vocabulary
- Sum
- The sum is the answer you get when numbers are added together.
- Addend
- An addend is a number that is being added.
- Pair
- A pair is a set of two numbers or objects grouped together.
- Make 10
- Make 10 means choosing two numbers that add up to 10 before adding the rest.
- Counters
- Counters are small objects used to show and count numbers.
Common Mistakes to Avoid
- Counting all counters one by one every time: this is slower and can lead to skipped or double-counted counters.
- Adding the numbers in the order they appear only: this misses easier pairs like 8 + 2 or 6 + 4.
- Forgetting to add the third number: after making 10, the remaining number still needs to be added.
- Moving counters without keeping all groups included: the total changes if a counter is left out or counted twice.
Practice Questions
- 1 Use the make 10 strategy to solve 8 + 2 + 5.
- 2 Add by grouping an easy pair first: 6 + 4 + 7.
- 3 Mia has 5 red counters, 3 blue counters, and 5 green counters. Which two groups would you add first, and why?