1题
2-6/13÷9/26
=2-6/13×26/9
=2-4/3
=2/3
2题
6/7×(4/5-2/3)÷1/5
=6/7×(4/5-2/3)×5
=5×6/7×(4/5-2/3)
=5×6/7×4/5-5×6/7×2/3
=24/7-20/7
=4/7