To make salad dressing, combine one tablespoon of oil for every two tablespoons of vinegar. If a batch of salad dressing has four tablespoons of oil, how many tablespoons of vinegar does it have?
Since the ratio is 1:2 (oil:vinegar), if there are four tablespoons of oil, there would be two tablespoons of vinegar (1/2 of 4).
Therefore, the batch of salad dressing has 2 tablespoons of vinegar.