To find the percentage difference between two numbers, we first need to calculate the absolute difference between them. In this case, the absolute difference between 40 and 50 is 10.

Next, we need to find the average of the two numbers, which is (40+50)/2 = 45.

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

So, the percentage difference between 40 and 50 is (10/45) x 100 = 22.22%.

This means that the difference between 40 and 50 is 22.22% of their average value.