$解：成人每次最少口服??\frac {400\ \text {mg}}{4×100\ \text {mg}}=1??片$
$成人每次最多口服??\frac {1000\ \text {mg}}{3×100\ \text {mg}}≈3??片$
$所以成人每次應(yīng)該口服?1～ 3?片。$
$兒童每次口服??\frac {20 \mathrm{kg}×10\ \text {mg/kg}}{4×100\ \text {mg}}=0.5??片$
$答：成人每次應(yīng)該口服?1～ 3?片，體重為?20kg?的兒童每次應(yīng)該口服?0.5?片。$
