How Many Ways to Choose Two People from Four

Choosing Two from Four

Two people are chosen from A, B, C and D. How many ways are there?

A with B and B with A are the same pair, so each pair is counted once. The second name is taken only from the ones after the first, and D has no one after it, so no branch grows from it. That leaves 6, exactly half of the 12 you get when the order matters.