2. Addition and subtraction

Lesson

When we add numbers together, place value is really important. Do you remember how to add numbers with three or more digits together?

Let's find the value of 705 + 205, by partitioning the numbers.

a

Fill in the box with the missing number.

705 = 700 + ⬚

Worked Solution

b

Fill in the box with the missing number.

205 = ⬚ + 5

Worked Solution

c

Find the value of 705 + 205.

Worked Solution

Idea summary

Addition by partitioning involves splitting numbers into each place value. The place values are then added separately.

When we subtract, we may need to regroup, or trade, some of our numbers. This video shows how we can do that, so that we can subtract another number. Let's take a look.

Find the value of 355-237.

Worked Solution

Idea summary

We always start from the ones place, when we work in a vertical algorithm. If we don't have enough to subtract, we can regroup from the next place to the left.

This time we have numbers with more digits, and the video shows how we can trade, or regroup, thousands to help us subtract in the hundreds place.

Find the value of 6241-2319.

Worked Solution

Idea summary

If we don't have enough to subtract, we can regroup from the next place to the left.

uses mental and written strategies for addition and subtraction involving two-, three-, four and five-digit numbers