Answer:

12 x 6 x 2 gives the same result 144, whether it is calculated as (12 x 6) x 2 or 12 x (6 x 2).

But 12 ÷ 6 ÷ 2 is not so straight forward as (12 ÷ 6) ÷ 2 is 1, but 12 ÷ (6 ÷ 2) is 4.

An operation x is associative if, when three elements are combined, it does not matter how the brackets are placed.
(a x b) c = a x (b x c).

So multiplication is associative but division is not. Similarly the following example illustrate that addition is associative but that subtraction is not.

(12 + 6) + 2 = 20 = 12 + (6 + 2)
(12 - 6) - 2 = 4 but 12 - (6 - 2) = 8.