To find the percentage difference between two numbers, we first need to calculate the absolute difference between them. In this case, the absolute difference between 450 and 365 is 85.

Next, we need to find the average of the two numbers. The average of 450 and 365 is (450+365)/2 = 407.5.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 450 and 365 is (85/407.5) x 100 = 20.85%.

Therefore, the percentage difference between 450 and 365 is 20.85%. This means that the two numbers differ by approximately 21% of their average value.