Instalments
A standard method from Further applications: the steps and worked examples.
Steps
Total paid = down payment + (number of instalments × amount). Extra cost = total paid − cash price. If interest is involved, use the compound interest or GS sum formula.
Worked examples
Example 1: A phone costs $12 000 in cash, or 24 monthly instalments of $560 with no down payment.
Total = 24 × 560 = $13 440. Paying by instalments costs $1 440 more.
For the whole topic, read Further applications: key points, common mistakes and how the DSE tests it.