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 290 and 210 is 80 (290 - 210 = 80).

Next, we need to find the average of the two numbers. The average of 290 and 210 is (290 + 210) / 2 = 250.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 290 and 210 is (80 / 250) x 100 = 32%.

Therefore, the percentage difference between 290 and 210 is 32%. This means that the two numbers differ by 32% of their average value.