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 80 and 90 is 10.

Next, we need to find the average of the two numbers. The average of 80 and 90 is (80+90)/2 = 85.

Now, we can find the percentage difference by dividing the absolute difference by the average and multiplying by 100.

So, the percentage difference between 80 and 90 is (10/85) x 100 = 11.76%.

This means that 90 is 11.76% greater than 80.