（1）54又2/5除以17
54又2/5÷17
=272/5÷17
=16/5
=3又1/5
（2）1/2+1/6+1/12+1/20+1/30+1/42
=30/60+10/60+5/60+3/60+2/60+1/42
=50/60+1/42
=5/6+1/42
=35/42+1/42
=36/42
=6/7