So a Fighter 5 has a CR of 5 meaning that a group of 4 5th level adventurers opposing him have a challenging encounter (table 3-2 dmg, page 498) against him. According to that logic a 5th level character is a challenging opponents for 4 5th level Fighters?:S? Is this correct? Have I calculated something wrong according to RAW? If that's the case, how can I calculate what level should my npc Fighter be to challenge a group of 4 5th level adventurers?