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 156 and 40 is 116.

Next, we need to find the average of the two numbers. The average of 156 and 40 is (156+40)/2 = 98.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 156 and 40 is (116/98) x 100 = 118.37%.

Therefore, the percentage difference between 156 and 40 is 118.37%. This means that the two numbers are quite different from each other, with one being significantly larger than the other.