Rounding Decimals

Objectives

To be able to round decimals up or down to the nearest whole number and to understand mathematical terms such as ‘1-place decimals’.

Resources

Abacus 4 Textbooks 2 & 3 | Squared paper | Rounding Decimals (MyMaths)

Today's Lesson

Main Activity

Turn to page 95 in Abacus 4 Textbook 2 for the mental warm-up exercise for today’s lesson. This marks the end of Abacus 4 Textbook 2.

Turn to page 20 in Abacus 4 Textbook 3.

Point out to your student that, in these numbers, there is only one digit after the decimal point. We call this a ‘1-place decimal’. It is also sometimes referred to as a number ‘to one decimal place’.

Remind your student that this digit is in the tenths column for place value: it represents tenths of the whole number.

Run through activities 1-6 on Rounding Decimals (MyMaths)

Just as when rounding with whole numbers, the ‘magic’ number that determines whether to round up or down is ‘5’. If the 1-place decimal is 1, 2, 3 or 4 (or any number less than 5), you round down to the whole number shown.

For example, 3.1 rounds down to 3 because ‘1’ is less than ‘5’.

However, 3.5 would round up to the next whole number, 4, because ‘5’ is equal to or greater than 5.

Once your student has understood the concept, ask them to copy and complete the page on squared paper. (Note that a 1-place decimal number is a number with one digit after the decimal point, e.g. 4.5 is a 1-place decimal number. 4.55 is a 2-place decimal number, and so on).

Next, discuss the ‘Think’ question with your student and remind them that potential answers will also include rounding down to 10, as well as rounding up from 9.

Extra Activities

You might like to try the homework activity on the My Portal section of MyMaths to practise this skill further.

MyMaths Homework - Rounding decimals

Citations

[1] app.mymaths.co.uk [2] app.mymaths.co.uk