Functional answer to Naresh Jain's challenge using Jedi

gistfile1.java

int calculateAveragePreviousPercentageComplete() { return reduceAndAverageActivitiesBy(PREVIOUS_PERCENTAGE_COMPLETE); }
int calculateAverageCurrentPercentageComplete() { return reduceAndAverageActivitiesBy(CURRENT_PERCENTAGE_COMPLETE); }
int calculateAverageProgressPercentage() { return reduceAndAverageActivitiesBy(PROGRESS_PERCENTAGE); }	

int reduceAndAverageActivitiesBy( Functor2<Integer, StudentActivityByAlbum, Integer> functor){
    return fold(0, activities, functor) / activities.size(); }

static final Functor2<Integer, StudentActivityByAlbum, Integer> PREVIOUS_PERCENTAGE_COMPLETE = 
    new Functor2<Integer, StudentActivityByAlbum, Integer>(){
        @Override public Integer execute(Integer accumulator, StudentActivityByAlbum value) { 
            return accumulator + value.getPreviousPercentageCompleted(); }};

static final Functor2<Integer, StudentActivityByAlbum, Integer> CURRENT_PERCENTAGE_COMPLETE = 
    new Functor2<Integer, StudentActivityByAlbum, Integer>(){
        @Override public Integer execute(Integer accumulator, StudentActivityByAlbum value) { 
            return accumulator + value.getPercentageCompleted(); }};

static final Functor2<Integer, StudentActivityByAlbum, Integer> PROGRESS_PERCENTAGE = 
    new Functor2<Integer, StudentActivityByAlbum, Integer>(){
        @Override public Integer execute(Integer accumulator, StudentActivityByAlbum value) { 
            return accumulator + value.getProgressPercentage(); }};