You might notice that sometimes the standard algorithm is called the 'vertical algorithm'. Let's think about why. When we use the standard algorithm, we line our numbers up in 'vertical' place value columns.

Subtraction with regroup

Let's see what we need to do when we don't have enough in one of our place value columns to subtract.

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Examples

Example 2

Find the value of 58 - 29.

Worked Solution

Create a strategy

Use the subtraction algorithm with regrouping.

Apply the idea

Write the subtraction in a vertical algorithm.\begin{array}{c} & &5 &8 \\ &- &2 &9 \\ \hline & \\ \hline \end{array}

Begin with the ones column. Since we don't have enough ones to subtract 9 from 8, we need to trade 1 ten from the tens place. \begin{array}{c} & &4 & \text{}^1 8 \\ &- &2 &9 \\ \hline & & \\ \hline \end{array}

Now we can subtract 9 from 18 in the ones column and 5 tens becomes 4 tens.\begin{array}{c} & &4 & \text{}^1 8 \\ &- &2 &9 \\ \hline & & & 9 \\ \hline \end{array}

Then subtract the numbers in the tens column, 4- 2 = 2.\begin{array}{c} & &4 & \text{}^1 8 \\ &- &2 &9 \\ \hline & &2 & 9 \\ \hline \end{array}

So, 58 - 29=29.

Idea summary

We always start from the ones place, when we work down our page. If we don't have enough ones to subtract, we need to trade from the tens place.

A vertical algorithm for 43 take away 37. Ask your teacher for more information.

Outcomes

VCMNA133

Recall addition facts for single-digit numbers and related subtraction facts to develop increasingly efficient mental strategies for computation

4.06 Subtraction with regrouping

Ideas

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Examples

Example 1

Subtraction with regroup

Examples

Example 2

Outcomes

VCMNA133

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