Update weightedAverage.md

snippets/weightedAverage.md

@@ -1,17 +1,27 @@
 ---
 title: weightedAverage
-tags: math,array,beginner
+tags: math,array,intermediate
 ---
 
 Returns the weighted average of two or more numbers.
 
-- Use `Array.prototype.reduce()` to add each value to an accumulator, initialized with a value of `0` and divide by the `length` of the array.
+- Use `Array.prototype.reduce()` to create the weighted sum of the values and the sum of the weights.
+- Divide them with each other to get the weighted average.
 
 ```js
-const weightedAverage = (nums, weights) => 
-  nums.reduce((acc, n, i) => acc + (weights[i] * n), 0) / nums.length;
+const weightedAverage = (nums, weights) => {
+  const [sum, weightSum] = weights.reduce(
+    (acc, w, i) => {
+      acc[0] = acc[0] + nums[i] * w;
+      acc[1] = acc[1] + w;
+      return acc;
+    },
+    [0, 0]
+  );
+  return sum / weightSum;
+};
 ```
 
 ```js
-weightedAverage([1, 2, 3], [0.6,0.2,0.3]); // 0.6333
+weightedAverage([1, 2, 3], [0.6,0.2,0.3]); // 1.72727
 ```