### Theory:

Regrouping the whole numbers does not change the value of the sum or the result. This is called the associative property.
This property applies only to operations such as addition and multiplication.
While adding (or) multiplying three or more whole numbers, the change in grouping of the whole numbers will not change the result.
Consider $$a$$, $$b$$ and $$c$$ are whole numbers then:

Example:
i)

ii)
This property does not apply to operations such as subtraction and division.
While subtracting (or) dividing three or more whole numbers, the change in grouping of whole numbers will change the result.
Consider $$a$$, $$b$$ and $$c$$ are whole numbers then:

Example:
$\begin{array}{l}i\right)\phantom{\rule{0.147em}{0ex}}\left(10-5\right)-1\ne 10-\left(5-1\right)\\ \\ 5-1\ne 10-4\\ \\ 4\ne 6\end{array}$

$\begin{array}{l}\mathit{ii}\right)\phantom{\rule{0.147em}{0ex}}\left(20÷10\right)÷2\ne 20÷\left(10÷2\right)\\ \\ 2÷2\ne 20÷5\\ \\ 1\ne 4\end{array}$