Subtracting one number from another
Recognising the importance of number order
Developing strategies for subtraction by:
Introducing vocabulary related to subtraction.
- counting back in ones using a number line
- subtracting 10s from multiples of 10
- counting back in tens
- recognising that subtracting by zero makes no difference
Key vocabulary: take away, subtract, subtraction, minus, from, -, =, leaves, result, less
Resources: 1-100 grid, 0 - 99 grid, quiz cards
This television programme introduces concepts of subtraction and related vocabulary. The strategies focused on are counting back in ones and tens using a number line or hundred square for support. Children should be encouraged to look for patterns in subtraction and talk about their methods. They need to be aware of the importance of the order of the numbers - unlike addition, subtraction cannot be carried out in any order. It is useful to encourage children to recognize that while the result is usually less, this is not always the case e.g. when subtracting zero, in order not to develop misconceptions that may have an impact on their later mathematics learning.
Counting back in ones and tens whole class or group work
Children need to be confident in counting back in ones and tens to be able to use the strategies efficiently. During the mental/oral part of the lesson, encourage the children to count backwards (as well as forwards) in both ones and tens from different starting numbers. Use models of the number system, such as number lines and hundred grids to enable children to make links between the aural and visual patterns in numbers.
Ask a child to choose a number that has specific properties e.g. a number that is more than 30, less than 50, ends in a zero, an odd number, an even number etc. and find it on the 0-99 grid. Challenge the children to count back/subtract an amount (e.g. 6, 10, two lots of ten etc.) from the number. Include subtracting zero in the challenge. Encourage the children to explain how they worked it out.
Quiz cards - individual or group work
This activity is designed to develop an understanding and use of the vocabulary involved in subtraction and addition. Brainstorm the different words for subtraction and put up a display of these words (alongside a display of addition words) adding new words as they arise. Ask the children to make up quiz questions using the quiz cards and putting numbers in the boxes. Work out the answers and write these on the back of the cards. Collect up the cards and use them for a class or group quiz.
Cut out the cards. Make up quiz questions using the cards and putting numbers in the boxes. Work out the answers and write these on the back.
What is ___ sutract ____ ?
What is ___ less than _____ ?
What does ___ minus ____ equal?
What do you need to subtract from ____ to leave ____ ?
What is the result of ____ take away ____ ?
What do _____ add _____ equal?
What is the total of _____ and _____ ?
What is _____ less than _____ ?
What do you need to add to _____ to make _____ ?
Which is more: the sum of _____ + _____ or the sum of _____ + ____ ?