To find the percentage difference between two numbers, we first need to find the absolute difference between them. In this case, the absolute difference between 400 and 361 is 39.

Next, we need to find what percentage this difference is of the original number. To do this, we divide the absolute difference by the average of the two numbers (in this case, (400+361)/2 = 380.5) and then multiply by 100.

So, the percentage difference between 400 and 361 is:

|400-361| / ((400+361)/2) x 100
= 39 / 380.5 x 100
= 10.25%

Therefore, the percentage difference between 400 and 361 is 10.25%. This means that 361 is 10.25% less than 400.