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 350 and 280 is 70 (350 - 280 = 70).

Next, we need to find the average of the two numbers. The average of 350 and 280 is (350 + 280) / 2 = 315.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 350 and 280 is (70 / 315) x 100 = 22.22%.

Therefore, the percentage difference between 350 and 280 is 22.22%. This means that the two numbers differ by 22.22% of their average value.