Added AverageMedian function

Maths/AverageMedian.js

@@ -0,0 +1,39 @@
+/*
+ * function averageMedian
+ * to find the median value of an array of numbers
+ * the numbers in an array will be sorted in ascending order by the function sortNumbers
+ * if the length of the array is even number, the median value will be the average of the two middle numbers
+ * else if the length of the array is odd number, the median value will be the middle number in the array
+ */
+
+ /*
+  * Doctests
+  * 
+  * > averageMedian([8, 9, 1, 2, 5, 10, 11])
+  * 8
+  * > averageMedian([15, 18, 3, 9, 13, 5])
+  * 11
+  * > averageMedian([1,2,3,4,6,8])
+  * 3.5
+  */
+
+function averageMedian(numbers) {
+    let median = 0; const numLength = numbers.length
+    numbers = numbers.sort(sortNumbers)
+    
+    if (numLength % 2 === 0) {
+        median = (numbers[numLength / 2 - 1] + numbers[numLength / 2]) / 2
+    } else {
+        median = numbers[(numLength - 1) / 2]
+    }
+    
+    return median
+}
+
+function sortNumbers(num1, num2) {
+    return num1 - num2
+}
+
+console.log(averageMedian([8, 9, 1, 2, 5, 10, 11]))
+console.log(averageMedian([15, 18, 3, 9, 13, 5]))
+console.log(averageMedian([1,2,3,4,6,8]))