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Software ==>	PowerPivot (72 exercises)
Topic ==>	The CALCULATE function (15 exercises)
Level ==>	Harder than average
Subject ==>	Power BI training

Use AVERAGEX to find average ratios, then CALCULATE to avoid divide-by-zero errors

This exercise is provided to allow potential course delegates to choose the correct Wise Owl Microsoft training course, and may not be reproduced in whole or in part in any format without the prior written consent of Wise Owl.

Before you can do this exercise, you'll need to download and unzip this file .

If you haven't already done so, run the SQL script in the above folder (copying and commercial use prohibited) to generate a database called MAM.

Create a new workbook, and in this create the following PowerPivot data model:

Import two tables: centres and centre types.

Create a pivot table showing the average square metre area for centre types, and also the average number of units:

The figures by type of centre.

No need to create any calculated fields for this: you can just include the relevant fields in the VALUES section of the pivot table and change the Value Field Settings so that Excel averages, not sums, the data.

Now create a calculated field called FalseAverage which divides one of these implicit measures by the other:

The implicit measures will appear in autocompletion.

This gives you the average ratio of floor area to number of units, but it's wrong:

The true average for any cell should be the average of the total square metres for that cell's query context divided by the total number of units for that cell's query context.

Create a calculated field called TrueAverage which uses the AVERAGEX function to calculate the average of the metres-to-units ratio:

The figures are different.

The shopping centre figures are returning an error because one of the centres (Market Quay, as it happens) has 0 units in the database. To get round this, amend your true average so that it omits any figures where the number of units is 0.

You can do this by wrapping your AVERAGEX function in a CALCULATE one.

The final figures should look like this: