（2/15+3/4+5/12）乘60=2/15乘60+3/4乘60+5/12乘60=8+45+25=685/27乘（1/4+1/5）=5/27乘1/4+5/27乘1/5=5/108+1/27=5/108+4/108=9/108=1/127/4乘17-3/4=(1/4)(7×17-3)=(1/4)×116=29