Content description

Add and subtract decimals, with and without digital technologies, and use estimation and rounding to check the reasonableness of answers (ACMNA128)

Elaborations

• extending whole-number strategies to explore and develop meaningful written strategies for addition and subtraction of decimal numbers to thousandths
• exploring and practising efficient methods for solving problems requiring operations on decimals, to gain fluency with calculating with decimals and with recognising appropriate operations

Source: Australian Curriculum, Assessment and Reporting Authority (ACARA)

Adding and subtracting decimals

Adding and subtracting decimals requires a clear understanding of place value.

In essence, it is the same process used to add and subtract whole numbers as long as we understand that the place value parts and the decimal points need to be aligned in the addition and subtraction process.

Adding decimals

When we add the decimal numbers 453.741 and 136.157, we set out the calculation making sure that the place value parts and the decimal points are lined up.

Decimal place value

	H	T	O		stenths	hundredths	thousandths
	4	5	3	.	7	4	1
+	1	3	6	.	1	5	7
=	5	8	9	.	8	9	8