Head Cases

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Purpose

This is a level 3 number activity from the Figure It Out series. It relates to Stage 6 of the Number Framework. 

A PDF of the student activity is included.

Achievement Objectives
NA2-1: Use simple additive strategies with whole numbers and fractions.
Student Activity

  

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Specific Learning Outcomes

solve subtraction problems using mental strategies

Required Resource Materials

FIO, Level 3-4, Number, Book 1, Head Cases, page 13

Activity

This activity encourages students to think through strategies that they could use to mentally solve subtraction problems.
All of the strategies shown require the students to think about the numbers involved in the calculation. This increases their number sense. With increased number sense and understanding, they can learn and even devise alternative strategies for solving number problems in other situations. Solving problems mentally improves number skills more than the vertical forms of working that have traditionally been taught.
The students’ preferred methods will usually depend on their previous experience, so some may revert to the vertical form whenever possible. However, even when the students can competently perform the vertical form of working, there is considerable value in looking at, teaching, and encouraging them to devise alternative strategies.
Students might look at the problem in question 1a this way:
923 – 598 = 900 – 600 + 23 + 2
= 325.
They might look at question 2c in a similar way:
502 – 286 = 500 – 200 + 2 – 86
= 216.
These strategies do not necessarily make the task easier, but they are both valid and worth considering in terms of why they work.

Answers to Activity


1. a. Scott:
923 – 598 = 
923 – 600 = 323
323 + 2 = 325
Stacey:
923 – 598 =
598 + = 923

jumps.
2 + 300 + 23 = 325
Kingi:
923 – 598 = 
923 – 500 = 423
423 – 90 = 333
333 – 8 = 325
b. Discussion points will vary.
2. Methods will vary. Answers are:
a. 551
b. 273
c. 216
d. 459
e. 436
f. 619
g. 251
h. 778

Attachments
HeadCases.pdf326.14 KB
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