This is a level 2 number link activity from the Figure It Out series. It relates to Stage 5 of the Number Framework.

A PDF of the student activity is included.

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use number lines to show mental strategies for addition and subtraction problems

FIO, Link, Number, Book One, Absolutely Abseiling, page 19

The cliff-face context of this activity is easily visualised as a vertical number line. The activity builds on the mental strategies for subtraction developed in the activity on the previous page.

Discuss the strategies presented in the speech bubbles. Have the students explain how the strategies chosen relate to a number line and why each one could be an easy way of working out the distances mentally.

If the students want to work out the problems on paper, remind them that it would not be possible to do this while abseiling, so they should put themselves in Edmund’s place and work the distances out mentally.

Challenge the students to come up with two or three different ways of working out the jumps. Ideas might include:

For question 3a: “45 metres take away 20 metres is 25 metres, so going back 3 metres to get to 28 metres means a total of 17 metres.”

Another way could be: “45 metres take away 10 metres is 35 metres, another 5 metres makes 30 metres and another 2 makes 28. So, I jumped 10 and 5 and 2, which makes 17 metres.”

For question 3b: “70 take away 35 is 35, so 71 metres take away 35 metres would be 36 metres. So the answer is 35 metres.”

Another way could be: “71 minus 1 makes 70, minus another 30 makes 40, and another 4 takes it to 36 metres. So 1 + 30 + 4 = 35 metres.”

A third way may be: “71 take away 40 is 31, go back 5 makes 36. So 40 – 5 = 35 metres.”

#### Answers to Activity

1. 16 m

2. 28 m

3. Answers and possible number lines are: