The percentage difference between 3 and 18 is calculated by finding the absolute difference between the two numbers, which is 15, and then dividing it by the average of the two numbers, which is (3+18)/2 = 10.5.

So, the percentage difference is (15/10.5) x 100% = 142.86%.

This means that 18 is 142.86% more than 3, or in other words, 18 is 242.86% of 3.

To understand this concept better, let's take an example. Suppose you have two stores, Store A and Store B, and you want to compare their sales.

Store A has a sales of $1000 and Store B has a sales of $1500. The absolute difference between the two sales is $500.

To find the percentage difference, we need to divide this difference by the average of the two sales, which is ($1000+$1500)/2 = $1250.

So, the percentage difference between the two stores is (500/1250) x 100% = 40%.

This means that Store B has 40% more sales than Store A.

I hope this explanation helps you understand the concept of percentage difference better.