To understand the percentage difference between two numbers, we first need to know what percentage means. Percentage is a way of expressing a number as a fraction of 100. For example, 50% means 50 out of 100 or 0.5 as a decimal.

Now, let's look at the two numbers given in the problem - 317 and 400. To find the percentage difference between them, we need to first find the absolute difference between the two numbers. Absolute difference means the difference without considering whether the numbers are positive or negative.

So, the absolute difference between 317 and 400 is:

400 - 317 = 83

Now, we need to find the percentage difference between these two numbers. To do this, we divide the absolute difference by the average of the two numbers and then multiply by 100 to get the percentage.

The average of 317 and 400 is:

(317 + 400) / 2 = 358.5

So, the percentage difference between 317 and 400 is:

(83 / 358.5) x 100 = 23.16%

Therefore, the percentage difference between 317 and 400 is 23.16%. This means that the difference between the two numbers is 23.16% of the average of the two numbers.