What am I doing wrong here?

You're very close. You're using numbers where you should be using number:

numbers.forEach( number => times5.push(number * 5));

The forEach method is going to:

• loop through each item in the array
• invoke a callback that you pass in
• pass the item as an argument into that callback.

So in this case, we're passing in an anonymous arrow function: number => times5.push(number * 5). number is the parameter we're giving that function, and then using in the body of that function. It might clarify something if we define that function somewhere else and then pass it in as the argument to forEach:

const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];

function multiplyByFiveAddToList(num) {
  times5.push(num * 5)
}

numbers.forEach(multiplyByFiveAddToList);

So in the example above I'm defining a new function multiplyByFiveAddToList. Then when I call forEach, it takes a function as an argument, I pass in the function I defined called multiplyByFiveAddToList. Then, it will loop through each item in the array and call that function, passing in the item.

forEach is an example of a higher order function. They're a tricky concept to wrap your head around. But it will help you understand what's going on when you're written your own higher order functions, not just using higher order functions that come automatically with JavaScript.

There are a few other courses at Treehouse that might help you with this topic:

Practice ForEach in JavaScript

JavaScript Array Iteration Methods

Asynchronous Programming with JavaScript

Your mistake is here:

times5.push(numbers * 5)

You are multiplying numbers * 5, and the correct should be number * 5.

So the correct anwers is this:

numbers.forEach( number => times5.push(number * 5));

More about the forEach method: https://www.w3schools.com/jsref/jsref_foreach.asp