Final answer:
Nellie serves 10 quarts of juice to the guests and has 2 quarts left.
Step-by-step explanation:
To find out how many quarts of juice are left, we need to first calculate the total amount of juice served to the guests. Nellie gives 2 cups of juice to each of the 20 guests, so the total amount of juice served is 2 cups/guest x 20 guests = 40 cups.
To convert the cups to quarts, we need to remember that there are 4 cups in 1 quart. So, 40 cups ÷ 4 cups/quart = 10 quarts of juice served.
To find out how many quarts of juice are left, we subtract the amount served from the total amount Nellie bought. Nellie bought 12 quarts of juice, so 12 quarts - 10 quarts = 2 quarts of juice left.