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 166 and 181 is 15.

Next, we need to find the average of the two numbers. The average of 166 and 181 is (166+181)/2 = 173.5.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 166 and 181 is (15/173.5) x 100 = 8.64%.

This means that the second number, 181, is 8.64% greater than the first number, 166.