Given
$$p = - 3 / 2, q = 4 / 5$$ and $$r = - 7 / 12$$
$$(p \div q) \div r \neq p \div (q \div r)$$
$$LHS = (p\div q) \div r$$
$$= (- 3 / 2 \div 4 / 5) \div (- 7 / 12)$$
$$= (- 3 / 2 \times 5 / 4) \div (- 7 / 12)$$
$$= - 15 / 8 \div - 7 / 12$$
$$= - 15 / 8 \times 12 / - 7$$
We get,
$$= - 45 / - 14$$
$$= \left \{- 45 \times (- 1)\right \} / \left \{- 14 \times (- 1)\right \}$$
$$= 45 / 14$$
Now,
$$RHS = p \div (q \div r)$$
$$= - 3 / 2\div (4 / 5) \div (- 7 / 12)$$
$$= - 3 / 2 \div (4 / 5\times 12 / - 7)$$
We get,
$$= - 3 / 2 \div 48 / - 35$$
$$= - 3 / 2 \times - 35 / 48$$
We get,
$$= 35 / 32$$
Therefore, $$LHS \neq RHS$$.