Final answer:
To complete the recipe, you need an additional 1/15 of a bag of flour.
Step-by-step explanation:
To find out how much flour you need for the recipe, you need to compare the amount you have (3/5 of a bag) with the amount required (2/3 of a bag).
You can find a common denominator for 3 and 5, which is 15. So, you have 9/15 of a bag and the recipe calls for 10/15 of a bag.
Therefore, you need an additional 1/15 of a bag of flour to complete the recipe.