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 31 and 49 is 18.

Next, we need to find the average of the two numbers. The average of 31 and 49 is (31+49)/2 = 40.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 31 and 49 is:

|31-49| / ((31+49)/2) x 100
= 18 / 40 x 100
= 45%

Therefore, the percentage difference between 31 and 49 is 45%. This means that 49 is 45% more than 31.