QYQ Set 4 -24

[lucyyeh]

A boy walking along a road at 3 kilometers per hour is overtaken by a truck traveling at 4 kilometers per hour. If the truck breaks down 1 kilometer beyond where it passes the boy, how many minutes after the breakdown does the boy reach the truck?

ANS: 18.5 mins

算式

設男孩在卡車出了故障後x分鐘到達卡車

3 X ( x/60+1/40) =1

x = 18.5

不解的是，這個算式中的1/40是什麼呢?

[dibert8]

卡車速度應該是 40 km/hr
卡車走 1 km, 男孩走 3/40 km, 卡車壞了就不再走.
假設男孩 t 小時追上卡車 => 3/40 + t = 1, t = 37/120 hr = 18.5 min