Subtraction

Objectives

To reinforce the method of counting up to find the answer to a subtraction calculation.

To apply knowledge of mathematical methods already learnt.

Resources

Abacus 4 Textbook 1 | Squared paper | Timestables (TopMarks) | Column addition (MyMaths) | Frog Method (YouTube)

Today's Lesson

Main Activity

Continue to learn the 2 times table, if necessary.

Practise counting back in ones for 10 from random 2 digit numbers. For example:

34, 33, 32...25, 24

77, 76, 75...68, 67

This video will talk you through counting back in 1s.

Look at the examples drawn on the number lines below which uses a number line to count on for subtraction. This method of counting up in order to work out subtraction sums is the most error-proof at this stage, as students can often find counting backwards a challenge.

The easiest method is to count up from the ones digit to the nearest 10, then count up to the next hundred and finally, to any remaining numbers. Remember to add the jumps to find the answer.

(If you need help with adding the jumps at the end, use Column addition (MyMaths) as a reminder.)

This method is also useful for mental calculations. Look at this step-by-step guide using a different example:

Watch Frog Method (YouTube) (which was introduced in previous lessons) for a further example if required.

Run through additional examples with your student until they are confident with the strategy.

Ask your student to copy and complete pages 8 and 9. In Q4-9 on both pages, your student must draw their own number line including the relevant numbers and jumps. Even if your student does not think they need the number lines to solve these calculations, encourage them to use them during this session as it shows the steps carried out mentally and will help identify any mistakes at this stage Encourage your student to work independently.

Citations

[1] youtu.be [2] www.youtube.com [3] www.topmarks.co.uk [4] app.mymaths.co.uk