Matching Pair Sums

Count how many pairs of scores in a list add up to a target value.

You are given a list of trivia scores in the order players answered, and a target sum. Look at every pair of positions in the list where the first position comes before the second. Count a pair every time the two scores at those positions add up to exactly the target. Return the total number of matching pairs. A single score can be part of many different pairs, and repeated values can each be counted separately.