So, imagine you have a big group of toys. There are different kinds of toys like cars, dolls, blocks, and puzzles. Now, let's say you want to play with only the cars and dolls. So, you need to take out only those toys from the big group that you want to play with. That means you are fitting a subgroup of toys that you like.
In the same way, when we talk about fitting subgroup in math, we mean that we want to look at only a certain part of a big group of numbers. We take out only those numbers that belong to a certain group we are interested in.
For example, let's say we have a big group of people's ages ranging from 1 to 100. But we want to study only the ages of people who are between 20 and 40 years old. So, we fit a subgroup of ages between 20 to 40.
Fitting subgroup is just like taking out only the things we need from a big group of things, so we can study or play with just the things we want.