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AS Level · Information Technology 9626

Using what-if analysis

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9.3 · Chapter 9 · AS Level IT · Hodder Education

Using What-If Analysis

How to build and test spreadsheet models, use Goal Seek to reverse-calculate target values, and use models to answer real what-if questions.

🎯 Goal Seek

🧪 Testing Models

🔢 Simple Numbers

📋 Test Plans

The Big Idea: What-if analysis lets you change inputs in a model and instantly see the effect on outputs. Goal Seek goes one step further — you specify what you want the output to be, and it finds the input value that achieves it. Always test the model with simple, known data before using it with real values.

9.3What-If Analysis in Practice

All computer models are based on what-if analysis — changing input values to explore different outcomes. In Excel, you change a cell value and all dependent formulas recalculate automatically. This makes it easy to explore many scenarios rapidly.

📦 The Widget Factory — Worked Example

Context: A factory makes widgets. Variables: cost of raw materials per widget, time to make each widget, number of workers, hours per day (8), order size, delivery deadline.

What-if question 1: "How many workers are needed to complete an order for 500 widgets placed on 7 January and required by 10 January?" (3 working days)

Approach: Enter 500 widgets in the order cell. Calculate days needed as a function of number of workers. Instead of guessing workers, use Goal Seek to find the exact answer.

Goal Seek result: 4.08 workers → round up to 5 workers (you can't employ 0.08 of a person) → 5 workers will complete the order in time with some capacity to spare.

What-if question 2: "What sales price per widget is needed to make a $50 profit on the order?" → Use Goal Seek again: set the profit cell to $50, changing the sales price cell → returns $3.77 per widget.

ToolGoal Seek

🎯 What is Goal Seek?

Goal Seek is a what-if analysis tool that enables you to find the input value needed to achieve a specific target output. Instead of changing inputs to see the resulting output (standard what-if), Goal Seek works in reverse: you specify the desired output and it calculates what the input must be.

When to use it: When you know the result you want a formula to produce, but you need to know what value to change to achieve it. For example: "What price must I charge per widget to make exactly $1,580 profit?" or "How many ingots must I produce to maintain my profit at $1,580 after a wage increase?"

Standard What-If Analysis

You change an input and observe the output change automatically.

Example: Change workers from 2 to 5 → see how many days the order will take.

Goal Seek (Reverse What-If)

You specify the desired output and Goal Seek finds the input needed to achieve it.

Example: Set days = 3 → Goal Seek finds that 4.08 workers are needed.

How to Use Goal Seek in Excel

Place cursor in the formula cell

Click on the cell containing the formula whose output you want to control — e.g. the cell showing number of days to complete the order (B12).

Open Goal Seek

Data tab → Forecast group → What-If Analysis icon → Goal Seek…

Set the target value

In the "To value:" box, enter the target output you want — e.g. 3 (the number of days available for delivery).

Specify the changing cell

"By changing cell:"

Click OK and interpret the result

9.3.1Testing the Spreadsheet Model

simple, known values

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