Add all the A tasks

Task/Averages-Arithmetic-mean/JavaScript/averages-arithmetic-mean-1.js

@@ -0,0 +1,11 @@
+function mean(array)
+{
+ var sum = 0, i;
+ for (i = 0; i < array.length; i++)
+ {
+  sum += array[i];
+ }
+  return array.length ? sum / array.length : 0;
+}
+
+alert( mean( [1,2,3,4,5] ) );   // 3

Task/Averages-Arithmetic-mean/JavaScript/averages-arithmetic-mean-2.js

@@ -0,0 +1,4 @@
+function mean(a)
+{
+ return a.length ? Functional.reduce('+', 0, a) / a.length : 0;
+}