Question

I understand the concept of adding full bar rest to other time signatures such as 6/4 but i can't figure out the maths for a bar of 5/4

Answer 1

The "z" key shortcut will give you a full-measure rest to place that will fill one measure, regardless of meter.

Note: for reference, this is covered on page 10.32 of the manual.  I point this out NOT to be the guy who answers "RTM" to every question (it's a big manual and it is easy to miss stuff), but because that section also provides other useful info on filling measures with rests.