Randomising questions
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    :kind: outline

Problem
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Want to randomise questions, so that some aspects are different for each student.

Randomised mathematical expressions can look odd.

Many common patterns:

* scenarios
* "random except for x"
* random distinct values
* generate a set of values satisfying a condition

Solution
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Define a list of variables, with implicit references between them.

Try to provide functions for common tasks.

Often, working backwards from a randomly-chosen result works better.

Instant preview of generated values is helpful.

Difficulties
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Some people prefer to work in a single plain text document, rather than the graphical interface. 
Is it possible to support them?

Picking fairly from all possibilities, e.g. pick a random prime number, would require calculating the whole set first.