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 425 and 340 is 85 (425 - 340 = 85).

Next, we need to find the average of the two numbers. The average of 425 and 340 is (425 + 340) / 2 = 382.5.

Now, we can find the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 425 and 340 is (85 / 382.5) x 100 = 22.22%.

Therefore, the percentage difference between 425 and 340 is 22.22%. This means that the two numbers differ by 22.22% of their average value.