You’ll need to use number_with_precision in your model’s get_invoice_amount_with_precision method. In order to make this accessible, you will need to include ActionView::Helpers::NumberHelper in your model:

```
class MyModel < ActiveRecord::Base
include ActionView::Helpers::NumberHelper
def get_invoice_amount_with_precision
number_with_precision(invoice_amount, :precision => 2, :delimiter => ',')
end
end
```