121212分之212121-2121分之1212

212121/121212=21*10101/(12*10101)=21/12=7/4
1212/2121=12*101/(21*101)=12/21=4/7
所以原式＝7/4-4/7＝49/28-16/28＝33/28

212121/121212 - 1212/2121
=21*10101/12*10101 -12*101/21*101
=21/12 -12/21
=7/4 -4/7
=49/28 -16/28
= 33/28