The national peanut board estimates it takes about 45 peanuts to make an ounce of peanut butter. How many more peanuts are in a 20 ounce jar than a 12 ounce jar?

1. Find the number of peanuts in a 20-ounce jar:
20 \text{ ounces} \times 45 \text{ peanuts/ounce} = 900 \text{ peanuts}

2. Find the number of peanuts in a 12-ounce jar:
12 \text{ ounces} \times 45 \text{ peanuts/ounce} = 540 \text{ peanuts}

3. Subtract the number of peanuts in the 12-ounce jar from the 20-ounce jar to find out how many more peanuts are in the 20-ounce jar:
900 - 540 = 360

Therefore, there are 360 more peanuts in the 20-ounce jar than in the 12-ounce jar.