1/5 ÷ [(2/3+1/5)x1/13]
=1/5÷(2/3+1/5)÷1/13
=1/5÷（10/15+3/15）÷1/13
=1/5÷13/15÷1/13
=1/5×15/13×13
=1/5×15
=3
也许不太好,没有功劳也有苦劳啊啊,