Tripods                                                               Number, Level 1

Problem
Tripods have three legs and are used to stand cameras on. If you had 18 legs, how many tripods could you make?

What is this problem about?
This problem involves forming groups of 3. Whether the children use repeated subtraction or repeated addition depends on the approach that they use. If they start with 18 legs and form groups of 3 until no legs are left they are modelling repeated subtraction. They are using repeated addition if they start with one tripod (3 legs) and keep adding groups of 3 until they have 18 in total.

Achievement Objectives
Number (Level 1)
- model and explain addition calculations with a sum of up to 20
or
- using up to 20 objects, model and explain subtraction calculations.

Mathematical Processes
- devise and use problem solving strategies (act it out, draw a picture, use equipment appropriately)

Resources required
tripod (or picture)
sticks or rods
Blackline master of problem (English)
Blackline master of the problem (Maaori)

Specific learning outcomes
The children will be able to:
- model and explain addition of sets of three or model and explain subtraction of sets of three
- count forward or back in threes

1. Show the children the tripod – count the legs, discuss its function.
2. Read the problem to the class.
3. Brainstorm for ways to solve the problem.
4. If the children suggest that they would like to use equipment ask them for ideas about what they think would be suitable.
5. Allow the children to work on the problem – individually or in small groups.
6. Circulate asking the children to explain their solutions.
7. Share solutions.

Extension to the problem
If you can see 27 legs, how many tripods are there?

Other contexts for the problem
Tricycles and wheels