根据题意，题目是这样的30/31÷63/62=30/31x62/63=（10x2）/（1x21）=20/21
30/31 ÷ 63/62= 30/31 x 62/63=20/2121分之20
30/31÷63/62=30/31×62/63=60/63=20/21
