4/9÷10/7＋5/9×7/10
=（4/9＋5/9）×7/10
=1×7/10
=7/10
1/12＋3/4×2/3÷2
= 1/12＋3/12
=4/12
=1/3
（1/2－5/11）×（5/9＋2/13）
=1/22*83/117
=83/2574