Lesson

When we work on subtraction problems, it helps to remember some of the addition strategies we've used so far.

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

To add large numbers, we can first partition the numbers and then add their partitions.

Find the value of 93 - 24.

Worked Solution

Idea summary

We can use a number line to subtract numbers, by plotting the first number and jumping left the number of spaces given by the second number.

We can also subtract using an algorithm, as we see in this video.

Find the value of 398 - 152.

Worked Solution

Idea summary

We can subtract two numbers using a vertical algorithm. We start at the units column and move left.

Let's take a look at how a vertical algorithm helps us solve subtraction with large numbers.

Find the value of 81\,579 -27\,398.

Worked Solution

Idea summary

When subtracting, especially when using the vertical algorithm, place value is really important. We want to make sure our numbers are lined up correctly before we subtract, and we start from the place to the far right.