### 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 $$0.01$$.

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 $\frac{22}{100}$, similarly $$0.67$$ can be written as $\frac{67}{100}$.

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.

Therefore, the total shaded region is the sum of $$0.22$$ and $$0.67$$. That is $$0.22 + 0.67 = 0.89$$.