A spreadsheet model represents a real situation with numbers and formulae, so you can ask "what if…?" without trying it for real. Each model here has inputs (the values you can change, tinted), calculations (formulae) and outputs (the results you care about, such as profit). Choose a model and a tool in the title bar.
- What-if analysis. Move a slider and every formula that depends on that input recalculates at once. The chart shows how one output changes across the whole range of one input.
- Goal seek works backwards: you choose the result you want (set cell to value) and the input to change (by changing cell), and the spreadsheet searches for the input that gives it, trying values and closing in. The steps it tried are listed. Some targets have two answers (a price that's too low and one that's too high can both give the same profit); goal seek finds the one nearer where it starts. Some can't be hit exactly, when the model rounds a value.
- Scenarios are saved sets of input values (best case, worst case…). Show one to load it into the model, and the scenario summary puts every scenario's inputs and outputs side by side, as a spreadsheet's scenario manager does.
Key ideas. A model is only as good as its rules and data: the ball model assumes the share of students who come falls steadily as the price rises, which is a guess. Models are used because they're cheaper, safer and quicker than trying things for real, but they simplify, so check their predictions against what really happens.
Common exam mistakes: confusing goal seek (you know the result you want and find the input) with what-if (you change an input and see the result); describing a scenario as one value rather than a set of input values; forgetting that a model's formulae and assumptions limit how far its answers can be trusted; mixing up fixed costs (which don't change with output) and variable costs.
Objective: Cambridge International AS Level IT (9626) spreadsheets: modelling, what-if analysis, goal seek, scenarios and charts; the advantages and limitations of computer models.
Where this fits
- Cambridge: Cambridge IGCSE Information and Communication Technology (0417); Cambridge A Level Information Technology (9626); Cambridge AS Level Information Technology (9626) Goes beyond Cambridge IGCSE Information and Communication Technology (0417): Goal seek and scenario summaries aren't in 0417; changing a model's inputs and the uses and limits of models are.
