Form 2 maths

Question

The diagram below shows the information about the journey of a car from town A to town D through town B and town C.

The speed from town B to town C is 10% more than from town A to town B. The speed from town C to town D is 25% more than from town B to town C. Calculate the average speed of the car from town A to town D.

Ans = 91km/h

Comments

A到B的速度 = 180km÷2.25（2 hours 15 minutes = 2.25 hours）= 80km/h

B到C的速度 = 80km/h×110% = 88km/h

B到C所需的时间 = 110km÷80km/h = 1.25h（也等于1小时15分钟）

C到D的速度 = 88km/h×125% = 110km/h

C到D的距离 = 110km/h×1.5 = 165km

Average speed = 总距离÷总时间

A到D的平均速度 = （180km+110km+165km）÷（2.25h+1.25h+1.5h{因为1 hour 30 minutes = 1.5h}）=91km/h

(●'◡'●)
Arghhhhhhhhhhhh又差一点

Answer 1

Speed from town A to town B

=180km ➗ 2 1/4h 

=180km ➗ 9/4

=180km ✖️4/9

=80 km/h

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The speed from Town B to Town C

=80km/h ✖️（100%+10%)

=80km/h ✖️110%

=80km/h ✖️11/10

=88km/h

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The time from Town B to Town C

=110km ➗ 88km/h

=5/4h

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The speed from Town C to Town D

=88km/h✖️（100%+25%）

=88km/h ✖️125%

=88km/h ✖️5/4

=110km/h

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The distance from Town C to Town D

=110km/h ✖️ 3/2 h

=165km

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Average speed

=(180km+110km+165km)➗（2 1/4h+1 1/4h+ 1 1/2h)

=455km ➗5h

=91km/h