
$\because 27 \gt 5\times 3$,
$\therefore 27$元可购买的商品一定超过了$5$件,
设买了$x$件.
$5\times 3+\left(x-5\right)\times 3\times 0.8\leqslant 27$,
$2.4x\leqslant 24$,
$x\leqslant 10$,
$\therefore $最多可购买该商品$10$件.

$\because 27 \gt 5\times 3$,
$\therefore 27$元可购买的商品一定超过了$5$件,
设买了$x$件.
$5\times 3+\left(x-5\right)\times 3\times 0.8\leqslant 27$,
$2.4x\leqslant 24$,
$x\leqslant 10$,
$\therefore $最多可购买该商品$10$件.