Theory:

A set of numbers is said to be associative for a specific mathematical operation if the result obtained when changing grouping (parenthesizing) of the operands does not change the result.
Rational Numbers:
 
i) Addition:
Changing the group of operands in addition of rational numbers does not change the result. Hence, rational numbers under addition are associative.
 
ab+cd+ef=ab+cd+ef
Example:
23+32+ (6)7 =23+32+ (6)7
ii) Subtraction:
Changing the group of operands in the subtraction of rational numbers changes the result. Hence, rational numbers under subtraction are not associative.
 
abcdef=abcdef
Example:
2332(6)72332(6)7
iii) Multiplication:
Changing the group of operands in the multiplication of rational numbers does not change the result. Hence, rational numbers under multiplication are associative.
 
ab×cd×ef=ab×cd+ef
Example:
23×32×(6)7=23×32×(6)7
iv) Division:
Changing the group of operands in the division of rational numbers changes the result. Hence, rational numbers under division are not associative.
 
ab÷cd÷ef=ab÷cd÷ef
Example:
23÷32÷(6)7=23÷32÷(6)7
Important!
Therefore for rational number addition and multiplication operations only satisfy the associative property, not the subtraction and division operations.