Is subtraction of decimals associative? if not, give a counter example.

Associative property is only applied to addition and multiplication. Thus, it can't be applied to subtraction. This property is manifested when you get the same answer no matter where you put the parenthesis. Example of associative property is:

(50 + 2) + (92 + 6) = 52+98 = 150
50 + (2+92) + 6 = 50 + 94 + 6 = 150

Here is the counter example for the subtraction of decimals:

(3.45 - 8.92) - (1.9 - 7.3) = -5.47 - ⁻5.4 = -0.07
3.45 - (8.92 - 1.9) - 7.3 = 3.45 - 7.02 - 1.9 = -5.47
As you can see, the answers are not the same.