# PRACTICE: Subtraction

Lesson

## Subtraction strategies

Let's go over some of the  subtraction strategies  we've looked at. These include:

• jumping back, using a number line

• bridging, or making up to 10

• using the answer to one problem to find the answer to another problem, by compensating

We also looked at how to use a  vertical algorithm  , writing our total first, then the number we are subtracting below it. This strategy can also be really useful if we need to  trade, or regroup  .

### Examples

#### Example 1

Use the number line to help you find the value of 35 - 24.

Worked Solution
Create a strategy

Plot the bigger number on the number line and count to the left by the smaller number.

Apply the idea

Plot 35 on the number line.

Jump 24 units to the left from 35. 24 is made up of 2 tens and 4 ones. So we can jump to the left by 2 tens and then 4 ones.

We end up at 11 on the number line. So: 35 - 24 = 11

#### Example 2

Find the value of 854 - 6.

Worked Solution
Create a strategy

Use the subtraction algorithm method.

Apply the idea

Write the subtraction in a vertical algorithm.\begin{array}{c} &8&5&4 \\ -& & &6 \\ \hline \\ \hline \end{array}

Begin with the ones column. Since we don't have enough ones to subtract, we need to trade 1 ten from the tens column. \begin{array}{c} & 8&4&\text{}^1 4 \\ -&&&6 \\ \hline \\ \hline \end{array}

Subtract the numbers in the ones column: 14-6=8.

\begin{array}{c} & 8&4&\text{}^1 4 \\ -&& &6 \\ \hline \ &&&8 \end{array}

Bring down the tens and hundreds place values.

\begin{array}{c} & 8&4&\text{}^1 4 \\ -&& &6 \\ \hline \ &8&4&8 \end{array}

#### Example 3

Find the value of 447 - 81.

Worked Solution
Create a strategy

Use the subtraction algorithm method.

Apply the idea

Write the subtraction in a vertical algorithm.\begin{array}{c} & 4 &4 &7 \\ -& &8 &1 \\ \hline & &&\\ \hline \end{array}

Subtract the numbers in the ones column: 7-1=6.\begin{array}{c} & 4 &4 & 7 \\ -& &8 &1 \\ \hline & &&6\\ \hline \end{array}

Next with the tens column, since we don't have enough tens to subtract, we need to trade 1 hundred from the hundreds column.\begin{array}{c} & 3 &\text{}^1 4 & 7 \\ -& &8 &1 \\ \hline & & &6 \\ \hline \end{array}

Then subtract the next place value, 14- 8 = 6, and bring down the hundreds place value.\begin{array}{c} & 3 &\text{}^1 4 & 7 \\ -& &8 &1 \\ \hline &3 &6 &6 \\ \hline \end{array}

So, 447- 81= 366.

Idea summary

When we are subtracting, we can't write our numbers in any order, like we can for addition. We must write the total, then the number we are subtracting, or taking away.

### Outcomes

#### MA2-5NA

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