2/3+3/5+5/6
=40/60+36/60+50/60
=126/60
=2又1/10
10-4/13-9/13
=10-(4/13+9/13)
=10-1
=9
6/7-3/8+1/8
=9/7-(3/8-1/8)\
=9/7-1/4
=36/28-7/28
=1又1/28
3.92/{1.75*（5.19-3.59）}
=3.92/(1.75*1.6)
=3.92/2.8
=1又2/5