Dave thinks he has a fantastic deal on his mobile phone: £20 per month with 1000 texts and 600 minutes of talk time. But he did have to pay for the phone? Fran thinks maybe an 18-month contract at £35 per month would have been better.
As Dave heads off to find out what some students think, Fran, using vivid graphics, gives an overview of straight-line graphs and plots a graph for the pay-as-you-go deal.
Dave and the students quickly work out that over 18 months the pay-as-you-go deal is cheaper than the contract, but what happens when you factor in 5p a day every time you use the internet?
Again, Fran uses straight-line graphs and their gradients to see how many days a month Dave can use the internet on his phone and still be better off.