AverageObservable.java

        Observable<Integer> numberObservable = Observable.fromArray(1, 2, 3, 4, 5);

        MathObservable.averageDouble(numberObservable)
                .subscribe(new Observer<Double>() {
                    @Override
                    public void onSubscribe(Disposable d) {

                    }

                    @Override
                    public void onNext(Double aDouble) {
                        System.out.println("Average: " + aDouble);
                    }

                    @Override
                    public void onError(Throwable e) {

                    }

                    @Override
                    public void onComplete() {

                    }
                });