Yesterday I shared with you the mental maths strategy of counting on. Today I want to look at the near doubles strategy. Most young children learn how to double numbers pretty quickly on their own. So how can we extend this and look at near doubles to help children be able to mentally calculate?
What is the near doubles strategy?
We use this strategy when adding two consecutive numbers, in other words two numbers that follow each other. This is where students use their knowledge of doubles to work out the answer. For example, the problem might be 5 + 6 =
This is the same as 5 + 5 + 1 = 11 or 6 + 6 – 1 = 11.
You could use a number line to demonstrate this to your students.
Using 100 grids to teach the strategy
For this activity you will need: 100-grids, enough for pairs of students as well as number cards with odd numbers between 20 – 100. You will also need a large 100 grid for the class to see.
- Whole class: Use a 100-grid and circle a pair of adjacent numbers. Ask students to add these and explain the strategy used for adding.
- Explain the near doubles strategy that could also be used. E.g: 24, 25. Double 25 and then adjust by 1.
- Again circle two different adjacent numbers and have the students use the near doubles strategy to add the numbers to find the answer.
- Pairs: Give each pair of students various numbers cards. They work with 100-grids to find adjacent numbers that add to the numbers on the cards given.
Another way to practice using the near doubles strategy is to add numbers in a triangle.
- Whole class: Write a 2 digit number on the board and ask the class for the next 2 numbers. E.g: 25, 26, 27
- Arrange the numbers in a triangle and ask for suggestions of different ways to add these numbers. Write the total in the center. Highlight the near doubles strategy.
- Pairs: Each player selects their own consecutive numbers and works out the total. They give their partner the total who needs to determine the 3 numbers. Exchange back and share solutions.
Tomorrow we’ll have a look at the compatible numbers mental maths strategy.
Graphic Credits: Graphics From the Pond