$$7 18 = .$$, and $$(7 18) 5 = .$$.
$$18 5 = $$, and $$(7 18) 5 = $$.
Is $$(7 18) 5 = 7 (18 5)$$ ?
$$\Rightarrow$$ Subtraction of whose numbers is not .
$$7 – 18 = - 11$$, and $$(7 – 18) – 5 = - 16$$.
$$18 – 5 = 13$$, and $$7- ( 18 – 5) = - 6$$.
Is $$(7 – 18) – 5 = 7 – (18 – 5)=$$ ?
No, $$(7 – 18) – 5 \neq 7 – (18 – 5)$$.
$$\Rightarrow$$ Subtraction of whole numbers is not associative.