Problems like 67 - … = 34

I am learning to solve problems like 67 – ? = 34 by solving 34 + ? = 67 or by finding 67 – 34.

First let’s look at an easy example with counters.

3 counters plus some more counters equals 7 counters

+ =

We can also change it around so it is a subtraction question.

=

The missing amount is obviously 4 counters.

Again, the missing amount is obviously 4 counters.

Changing subtraction questions into addition questions makes them easier to answer. We will use this strategy throughout this lesson.

……..

……..

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Zac had $84. After going shopping he had $52 left. 84 - …. = 52

Step 1: Change the question into an addition question.

Step 2: Choose an appropriate strategy to answer this question. I’m going to add the ones and tens separately but you might like to use a different method.

52 + …. = 84

I have 2 ones but need 4 ones. How many more ones do I need?

I have 5 tens but need 8 tens. How many more tens do I need?

2

3 tens (30)

Add them together. 30 + 2 = 32

So… 84 – 32 = 52 or 52 + 32 = 84

A netball team has 156 raffle tickets to sell. They sell some and have 119 left. How many have they sold? 156 - …. = 119

Step 1: Change the question into an addition question.

Step 2: Choose an appropriate strategy to answer this question. I’m going to use a number line but you might like to use a different method.

119 + …. = 156

119 156120

+36+1

Imagine a number line. On the number Line jump to the nearest tidy number.From here jump up to 156. Add your jumps together. This is the answer.

1 + 36 = 37

Now try these questions on your own. Remember to change them into addition questions first.

Need some more practise? Try Pg57 of Teacher Tools Addition and Subtraction Book Numeracy resources

1) 84 - ….. = 19

2) 236 - …. = 198

3) 276 - ….. = 233

4) 149 - … = 81

5) 549 - …. = 501

Click again when you have completed each question and the answer will be displayed.

19 + 65 = 84

198 + 38 = 236

233 + 43 = 276

81 + 68 = 149

501 + 48 = 549