function calculateAverage(arr) {
  let sum = 0;
  let count = 0;

  for (let i = 0; i < arr.length; i++) {
    if (arr[i] && typeof arr[i] === "number") {
      sum += arr[i];
      count++;
    }
  }

  return sum / count;
}

If we pass calculateAverage an array that contains a 0, because we’re filtering out falsy values (of which 0 is one), our calculation will be wrong.

To fix our function, we can get rid of our truthy check (arr[i]) and just verify the element is a number.

function calculateAverage(arr) {
  let sum = 0;
  let count = 0;

  for (let i = 0; i < arr.length; i++) {
    if (typeof arr[i] === "number") {
      sum += arr[i];
      count++;
    }
  }

  return sum / count;
}