我想问一道英文的数学题!.我要过程John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they
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我想问一道英文的数学题!.我要过程John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they
我想问一道英文的数学题!.我要过程
John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they from the house when Susan catches up to John, and how long after John fist left the house? 要用方程来解答
最后的fist应该是 first
我想问一道英文的数学题!.我要过程John leaves home and start walking at 4 km/h to his friend's house. Half and a hour later, his sister Susan leaves the house on a bicycle and heads in the same direction at 12 km/h. How far away are they
约翰从家里离开以4km/h的速度去朋友家一个半小时之后,他的姐姐苏珊骑车沿同一路线出发,速度为12km/h.问当苏珊追上约翰时离家多远,此时约翰离家多长时间?
当姐姐出发时弟弟走的路程：4*1.5=6（km）
姐姐追上弟弟所需时间：6/（12-4）=0.75（h） （追及问题）
这段时间里姐姐走了0.75*12=9（km） 即距家9km
所以弟弟走了9/4=2.25(h) (或1.5+0.75=2.5（h）)
答：——————————……
4*1.5=6km 6/（12-4）=0.75h 12*0.75=9km ∴离家9km 在john离开家0.75h后
设John离开家后x小时候Susan追上John,他们共行路程为s千米，由题可知
4x=12×(x-1,5)
=> x=9/4
s=4×9/4=9(km)
所以，John离开家2小时15分钟后Susan追上John，离家9千米。