Remainders are still very important and sometimes you can't replace them with a decimal number.
Example:
If you have 11 apples that need to be shared equally by 3 people, the answer is 11 divided by 3 or 11/3
However, in decimal it is 3.66666666666666666666666666...
The number of digits after the decimal never ends, so you can't ever do it exactly according to decimal math.
but by using remainders we get
3 with a remainder of 2. That is a real answer that can be presented in the real world as at least a partial answer. Each person in the group can have 3 whole apples. We now need to figure out how to divide the 2 remaining apples. Since it can't be done evenly, maybe the group just decides to stop at 3 per person to be 100% fair.
Decimals don't always work. Another good example are modern day computers that only use binary (1's and 0's). They can only do division math using remainders. These are later converted to decimal format to make it easier to read, but the computer chips all work with remainders. They have no other way of doing it. Computers would not work without remainders!
