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 90 and 170 is 80 (170 - 90 = 80).

Next, we need to find the average of the two numbers. The average of 90 and 170 is (90 + 170) / 2 = 130.

Now, we can find the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 90 and 170 is (80 / 130) x 100 = 61.54%.

This means that 90 is 61.54% less than 170, or that 170 is 61.54% more than 90.