To understand the percentage difference between two numbers, we first need to know what percentage means. Percentage is a way of expressing a number as a fraction of 100. For example, 50% means 50 out of 100 or 0.5 as a decimal.

Now, let's look at the numbers 73 and 100. To find the percentage difference between them, we need to first find the absolute difference between the two numbers. Absolute difference means the difference without considering whether the numbers are positive or negative. In this case, the absolute difference between 73 and 100 is 27.

Next, we need to find what percentage of 100 the absolute difference represents. To do this, we divide the absolute difference by the larger number (in this case, 100) and then multiply by 100 to get the percentage. So, the percentage difference between 73 and 100 is:

(27/100) x 100 = 27%

Therefore, the percentage difference between 73 and 100 is 27%. This means that 73 is 27% less than 100 or that 100 is 27% more than 73.