（2/5-1/3）÷5/6
=（2/5-1/3）×6/5
=2/5×6/5-1/3×6/5
=12/25-2/5
=12/25-10/25
=2/25
7.5+2.5÷0.5
=7.5+2.5×2
=7.5+5
=12.5
（5/6+1/4）×24
=5/6×24+1/4×24
=20+6
=26
4-5/13÷15/26-1/13
=4-5/13×26/15-1/13
=4-2/3-1/13
=4-26/39-3/39
=4-29/39
=3又10/39
8/9+6/7×2/3+3/7
=8/9+4/7+3/7
=8/9+1
=1又8/9
（4/5-2/3）÷（1/2+2/3）
=(30×(4/5-2/3）)÷(30×（1/2+2/3）)
=(24-20）÷(15+20）
=4/35