I would go for a simpler approach...

$collection = collect([
    ['value' => 10, 'coefficient' => 2],
    ['value' => 20, 'coefficient' => 3],
    ['value' => 30, 'coefficient' => 4],
]);

$temp = $collection->map( fn($x) => [
  'weight' => $x['coefficient'], 
  'weighted_value' => $x['value'] * $x['coefficient']
]);

$weightedAverage = $temp->sum('weighted_value') / $temp->sum('weight');

echo $weightedAverage; // Output: 22.222222222

Not sure whether it is computationally more heavy or not (please comment @larry), but from readability it is more clear. And the output is correct ;-)