the answer
equivalence of (pq)r and (qr)p
in mathematics, A is equivalent to B if
1) A implies B and B implies A,
or 2) A = B
one of these conditions must be proven to prove equivalence
(pq)r = (p x q) x r, by using associative property of the multiplication,
(p x q) x r = p x (q x r )
therefore,
(pq)r= (p x q) x r = p x (q x r )= (qr)p, that means (pq)r equivalent to (qr)p