Merge pull request #315 from casalazara/master

Create weighted_average.md

snippets/weighted_average.md

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+---
+title: weighted_average
+tags: math,list,intermediate
+---
+
+Returns the weighted average of two or more noumbers.
+
+- Use `sum()` to sum the products of the numbers by their weight and to sum the weights.
+- Use `zip()` and a list comprehension to iterate over the pairs of values and weights.
+
+```py
+def weighted_average(nums, weights):
+  return sum(x * y for x, y in zip(nums, weights)) / sum(weights)
+```
+
+```py
+weighted_average([1, 2, 3], [0.6,0.2,0.3]) # 1.72727
+```