The question says "EXCLUDING RVSM' .... so we need to look at the ICAO cruising levels schematic
.... look on the front of the E(HI)4/5 enroute chart -
you will see two levels schematics ....
- the left hand one says
'below FL290' .... ODD and EVEN make sense.
- the right hand on says 'at
or above FL290' .... here, ICAO rules change -
separation requirement
between opposite traffic is now 2000ft, hence separation
between traffic in the same direction is now 4000ft. This basically removes all
the mathematically EVEN levels ... 300, 320, 340 etc, BUT convention still
refers to ODD (290, 330, 370....) and EVEN (310, 350, 390....) levels.
You don't have to remember the numbers - you can
always refer to the chart ...