# Mobile Phones

Pupils compare two different mobile phone tariffs and decide when one is cheaper than the other.

# Practical details

Suitability
National Curriculum levels 6 to 7
Time
20 to 40 minutes
Resources
Pencil and paper; graph or squared paper should be made available and supplied on request

# Key Processes involved

Representing
Select a way of comparing two phone tariffs, for example, using an appropriate table or graph
Analysing
Explore the effect of varying the times of calls, working logically and recognising the impact of the constraints. Make accurate calculations or graphs, recording their methods systematically and deduce when one call plan is cheaper
Interpreting and evaluating
Interpret their tables and graphs to solve the problem, relating their findings to the original context
Communicating and reflecting
Communicate their reasoning and findings clearly

# Teacher guidance

Check that pupils understand the context; for example, show them examples of advertisements of pay as you go and other types of mobile phone tariffs.

• Who has a mobile phone? What kind of tariff are you on?
• How did you decide to go with that tariff?
• It can be very difficult to decide which mobile phone tariff is cheapest for you.
• In this task we compare two mobile phone tariffs.

Pupils can tackle this task in different ways, but higher ability pupils might be expected to:

• formulate and solve linear equations with whole-number coefficients
• use algebraic or graphical methods to solve simultaneous linear equations in two variables