1 设距离为L,则原预定乘公交用时T=L/30在路逗羡程的后半段,车速提升一倍为60km/h,比原来预定用时T/2少用0.25h(15min)则有方猜指戚程:L/2/60=T/2-0.25带入T=L/30,解得L=30km2 通讯员从穗陵排尾到排头是追击问题:t1=450/(3-1.5)=300s通讯员从排头到排尾是相遇问题:t2=450/(3+1.5)=100s总用时T=t1+t2=400s 望采纳..
L/2/60=T/2-0.25带入T=L/30,解得L=30km