The purpose of this activity is to engage students in using their knowledge of number operations to find an unknown.
This activity assumes the students have experience in the following areas:
The problem is sufficiently open ended to allow the students freedom of choice in their approach. It may be scaffolded with guidance that leads to a solution, and/or the students might be given the opportunity to solve the problem independently.
The example responses at the end of the resource give an indication of the kind of response to expect from students who approach the problem in particular ways.
I’m thinking of a number.
I get the same answer if I add 8 to my number, or if I don’t add 8 but instead I triple my number.
What number am I thinking of?
The following prompts illustrate how this activity can be structured around the phases of the Mathematics Investigation Cycle.
Introduce the problem. Allow students time to read it and discuss in pairs or small groups.
Discuss ideas about how to solve the problem. Emphasise that, in the planning phase, you want students to say how they would solve the problem, not to actually solve it.
Allow students time to work through their strategy and find a solution to the problem.
Allow students time to check their answers and then either have them pair share with other groups or ask for volunteers to share their solution with the class.
The student uses a systematic trial strategy, trying the counting numbers to find the unknown number. They organise the results in a table and look for patterns.
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The student conjectures that 4 is the missing number since twice the number equals 8. They check their conjecture by calculating 4 + 8 and 3 x 4 and getting the same result.
Printed from https://meaningfulmaths.nt.edu.au/mmws/nz/resource/what-s-my-number-1 at 8:50pm on the 26th February 2024