(4/13+1/17)×13+4除以17
=4+13/17+4/17
=4+17/17
=4+1
=5
1/3除以（2/3-2/5）×3/5
=1/3÷(4/15)×3/5
=1/3×15/4×3/5
=15/20
=3/4
楼上的13/7+4/7=1?怎么搞的?