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# Loops and arrays

`for`

loops are handy for traversing arrays.
In the following example, the elements of an array are added together:
```
let sum = 0;
for (let i = 0; i < myArray.length; i++) {
sum = sum + myArray[i];
}
```

## Exercise

Write a function

Example:

`mean`

that accepts an array filled with numbers
and returns the arithmetic mean of those numbers.Example:

`mean([1, 2, 3])`

should return `(1+2+3)/3`

= `2`

.
+ Hint

To calculate the mean of n numbers, you have to add up the numbers and divide the obtained sum by n.

+ Solution

```
function mean(data) {
let sum = 0;
for (let i = 0; i < data.length; i ++) {
sum = sum + data[i];
}
return sum / data.length;
};
```