(60+5)/(1-5/60)
=65/(1-1/12)
=65/(11/12)
=65*(12/11)
=780/11
=70又(10/11)分
到再次重合时需要70又(10/11)分
15/(1-5/60)
=15/(1-1/12)
=15/(11/12)
=15*(12/11)
=180/11
=16又(4/11)分
到时针与分针第一次成90°的角时需要16又(4/11)分