Simple functions to calculate weighted averages in Clojure

core.clj

(ns rubric.core)

(defn average
  "Averages a set of scores"
  [& scores]
  (/ (apply + scores) (count scores)))

(defn- sum-of
  "Sum the collection after applying the given function"
   [f coll]
   (->> coll 
        (partition 2) 
        (map f) 
        (apply +)))

(defn weighted-average 
  "Calculates a total score from individual weighted results.
  Expects pairs of <weight>, <score> whose weights add to 1.0."
  [& args]
  {:pre [(-> args count even?) 
         (= 1N (sum-of first args))]}
  (sum-of #(apply * %) args))

(defn- main 
  "A quick test of the weighted-average calculation"
  [& args]
  (println (weighted-average 4/10 (average 96 93.7 97.2 96.4 94.8)
                             3/10 50
                             2/10 80
                             1/10 75)))