A half-elf uses Knack for Success on a Ranger, who then uses Split the Tree:
Knack for Success: The target gains a +2 power bonus to his next attack roll [...]"
Split the Tree: Make two attack rolls, take the higher result, and apply it to both targets.
- The ranger rolls one d20 and adds the +2, then rolls the second one and takes the higher result.
- The dice are rolled at the same time and both gain the +2.
- The dice are rolled at the same time and the ranger applies the +2 to the higher.