Subtraction Using Decimals

Objectives

To use English money for working and subtracting with decimals.

To understand that any digit to the left of the decimal point is a whole number and that any digit to the right of the decimal point is a part of the whole.

Resources

Abacus 4 Textbook 2 | Squared paper | Finding Change using a Numberline (YouTube)

Today's Lesson

Main Activity

As a mental warm up, think of some measurements in metres that involve decimals and ask your student to convert them to metres and centimetres.

For example:

4.73m = 4m 73cm or 473cm.

Turn to page 50 in Abacus 4 Textbook 2.

Look at the questions on the page together. Point out to your student that all numbers to the left of the decimal point are whole pounds. Anything to the right of the decimal point represents pence – less than a whole pound. There are 100 pence to each pound. If your student is a little unfamiliar with the concept of English money, watch 'Money' to recap.

Using the Frog Method is an excellent method to find change. Watch Finding Change using a Numberline (YouTube) for examples.

Now look at Q1. Using the Frog method, count forward from the pence to the nearest whole pound, then jump to the next £10.00

For example:

If I spend £6.54, what is the change from £10?

£6.54 + £0.46 = £7.00

£7.00 + £3.00 = £10, so the answer would be that there is £0.46 + £3.00 = £3.46 change from £10.00

Once you feel that your student is comfortable with the concept, ask them to complete the calculations on the page. Remind your student to include a sentence answer to the word problems, as well as to include the unit of measure where required.

As before, drawing an empty number line may prove useful to keep track of amounts counted on during calculation.

Citations

[1] www.youtube.com [2] www.youtube.com