(1)甲、乙两人以不变的速度在环形路上跑步,相向而行,每隔40s相遇一次,已知甲跑一圈用60s,则乙跑一圈所用的时间是( )
A.40s B.100s C.120s D.60s
设一圈长度为S 乙跑一圈所用时间为X 则 S/60+S/X=S/40 解得X=120
C没错,40/60+120/40=1
选A啊....