f.2 maths 1題20分

2008-06-18 1:41 am

Amy and Ada both need to travel x km to go to school.
One morning, they set off at the sametime.
Amy walked at 5 km / h for 12 minutes,
and then got on a bus which travelled at 20km/h
for the rest of the journey.
Ada travelled the whole journey in a car at 30 km/h and arrived at
school 45 minutes before Amy.

(a) Find, in terms of x, the time taken by Amy and
that taken by Ada to get to school. (3 marks)

(b) Hence, find the value of x .

回答 (1)

Yoko

2008-06-18 3:52 am

✔ 最佳答案

(a)

【d＝v×t】

Let T hour be the time taken by Amy to get to school

x＝5×12÷60＋20×（T－12÷60）…1

x＝30×（T－45÷60）…2

From 1：

5×12÷60＋20×（T－12÷60）＝x
1＋20T－4＝x
∴T＝（x＋3）/20…3
【the time taken in terms of x by Amy】

From 3：

Ada arrived at school 45 minutes before Amy, hence

T＝（x＋3）/20－45/60
T＝（x＋3）/20－15/20
T＝（x＋3－15）/20
T＝（x－12）/20…4
【the time taken in terms of x by Ada】

(b)

From 4：

30×（x－12）/20＝x
30x－360＝20x
10x＝360
∴x＝36

【Amy and Ada both need to travel 36 km to go to school.
】

參考: Me, hope it helps

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