【答案】:
$20$,$5$,$800$,$30$,$4$,$2$。
【解析】:
$1$米$= 10$分米,$2$米換算成分米為:$2×10 = 20$分米;
$1$厘米$= 10$毫米,$50$毫米換算成厘米為:$50÷10 = 5$厘米;
$1$分米$= 100$毫米,$8$分米換算成毫米為:$8×100 = 800$毫米;
$1$分米$= 10$厘米,$3$分米換算成厘米為:$3×10 = 30$厘米;
$10$厘米$= 1$分米,$40$厘米換算成分米為:$40÷10 = 4$分米;
$10$分米$= 1$米,$20$分米換算成米為:$20÷10 = 2$米。