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 40 is 40 (80-40=40).

Next, we need to find the average of the two numbers. The average of 80 and 40 is (80+40)/2 = 60.

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 40 is (40/60) x 100 = 66.67%.

This means that the second number (40) is 66.67% less than the first number (80). Alternatively, we can say that the first number (80) is 66.67% more than the second number (40).