BASIC Dungeons and Dragons question

[Words Of Wisdom]

1 monster @ CR5 = EL5 = 4 PCs @ average level 5 should be able to handle it while expending 25% of their resources for the day (spells and the like).

2 monsters @ CR3 = EL5. There's a rule of thumb somewhere in the DMG about doubling the monsters adds 2 to the EL.

(EL = Encounter Level)