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

**LO: To add or subtract decimal numbers**

**Know:**

- how round numbers for estimation
- how to add numbers
- how to subtract numbers
- what the definition of sum is
- what the definition of difference is
- the place value of decimal numbers

**Understand:**

- that the addition of decimal numbers makes the number larger
- that the subtraction of decimal numbers makes the number smaller
- that adding or subtracting decimal numbers you need to make sure that you line up the decimal point properly.

**Do:**

- I can add and subtract decimal numbers

When adding decimal numbers make sure you always line up the decimal points.

When subtracting decimal numbers make sure you always line up the decimal points.

If there isn’t the same number of digits, then you need to add in 0s after the last digit. Remember adding zeros after the last digit doesn’t change the place value of the decimal number.

Rounding Decimals

Rounding decimals is fairly easy. There is just 1 simple rule, if the next number in line is equal or greater than >= 5 then you round the number up. If the next number in line is less than < 5, then you round the number down.