(30-15)/(1-5/60)=15/(1-1/12)=15*(12/11)=180/11=16又(4/11)分(30+15)/(1-5/60)=45/(1-1/12)=45/(11/12)=45*12/11=540/11=49又(1/11)分时针在6：16又(4/11)分和6：49又(1/11)分时,时针与分针成直角....