Theory:

Decimal grid or area models can be used to understand the process of addition and subtraction using decimal numbers.
Decimal grid:
The below the grids models are represents the decimal numbers \(1.0\), \(0.1\) and \(0.01\).
 
3.png
 
4.png
 
5.png
 
Now let us do the addition using these grids.
Example:
Find the sum of \(0.22\) and \(0.67\).
 
Here, \(0.22\) can be written as 22100, similarly \(0.67\) can be written as 67100.
 
In the grid model first shade the region of \(0.22\) followed by \(0.67\). Here we denote the decimal in different to understand it clearly.
 
6.png
 
Therefore, the total shaded region is the sum of \(0.22\) and \(0.67\). That is \(0.22 + 0.67 = 0.89\).