急 ! F5 Speed 計法1條唔識做 ?

我自己唔敢應叻，因為我嘅數學知識應該比您貧乏，或者以下答案我會計錯。

(a) （呢題可以唔駛睇圖，或者您都已經識計。）
Time required
= 4km÷10km/h
= 0.4h
=(0.4×60) mins
=24 mins

∴Rechel complete the first 4 km of journey at= 9:30＋24mins = 9:54


(b)（Rechel同Louis中途休息時間，即係幅圖打水平綫嘅部份）
Rachel starts taking a break at 9:54（即係(a)計算到嘅答案，幅圖示意Rachel喺呢段時間開始休息）
and she starts her second jorney at 11:09
∴The time required of the break taken by Rachel= 11:09－9:54= 1hr 15 mins= 75 mins

（至於Louis, 我認為喺 0嘅水平線並非佢嘅休息時段，所以我只係計上面嘅水平線）
Louis starts taking a break at 10:50 and he starts his second jorney at 11:20
∴The time required of the break taken by Louis= 11:20－10:50= 20 mins


(c) （Rachel同Louis相遇即係幅圖互相交叉嘅部份）
Louis starts his first journey from 9:54 to 10:50 for 7km.
i.e. He spends 56 mins for 7km
56 mins= 56/60 hrs= 14/15 hrs
∴Speed of Louis in his first journey= 7km÷14/15 hrs= 7.5 km/h
The speed of Louis keeps constant when he meets Rachel and he meets Rachel when walk for 6 km.
∴The time required for him to meet Rachel= 6 km÷7.5 km/h= 0.8 hrs=(0.8×60) mins= 48 mins
∴Rachel and Louis meet at= 9:54＋48 mins= 10:42