**Tell us what’s happening:**

Describe your issue in detail here.

So, as far as reading and understanding the code I’m stuck. I don’t understand where they got the n - 1. Why does multiply(arr, n) == multiply(arr, n - 1) * arr[n - 1]? and why can I use that in both an addition problem and a multiplication problem? That part isn’t explained and I don’t understand where they got it from.

```
**Your code so far**
```

```
function sum(arr, n) {
// Only change code below this line
if(n <= 0) {
return 0;
} else {
return sum(arr, n - 1) + arr[n - 1];
}
}
// Only change code above this line
```

```
**Your browser information:**
```

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36`

**Challenge:** Replace Loops using Recursion

**Link to the challenge:**