To find the percentage difference between 100 and 120, we first need to calculate the absolute difference between the two numbers.

The absolute difference between 100 and 120 is 20 (120 - 100 = 20).

Next, we need to find what percentage of 100 the absolute difference represents. To do this, we divide the absolute difference by 100 and then multiply by 100 to get the percentage.

So, (20 / 100) x 100 = 20%.

Therefore, the percentage difference between 100 and 120 is 20%. This means that 120 is 20% more than 100.

To summarize, the percentage difference between two numbers is calculated by finding the absolute difference between the two numbers, dividing it by the original number, and then multiplying by 100 to get the percentage.