Javascript Tutorial: Average Function over an Array

// Write a function that takes in an array of numbers and outputs the average of all the numbers.

// Ex:
// Input: [ 1 , 4 , 7 ]
// Output: 4

// Input: [ 10, 5 ]
// Output: 7.5

// Input: [ 1.5, 3, 2.5, 1 ]
// Output: 2