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Question

Please kindly advise whether the answer is correct? thank you in advance.

 

At 10 30 a bus started travelling from Town X at an average speed of 60km/h. at 1430, a car started from the same place, travelling on the same road at a constant speed. If the car took 4 hours to catch up with the bus, find the average speed of the car

the answer  120km/h ??????

 

Mrs Lee took 2 h to travel from Town P to Town Q. Her average speed for the whole journey was 80km/h. For the first 1/4 of the journey, she travelled at an average speed of 60km/h. find her average speed for the remaining journey.

Ans: 90km/h?????

Answer

At 1030 a bus started travelling from Town X at an average speed of 60 km/h. at 1430, a car started from the same place, travelling on the same road at a constant speed. If the car took 4 hours to catch up with the bus, find the average speed of the car.

1030 to 1430 ——- 4 h (bus started before the the car)
4 + 4 = 8 h(total travelling time of bus)
8 x 60 = 480 km (distance travelled by bus)
480/4 = 120

Ans : 120 km/h.

Mrs Lee took 2 h to travel from Town P to Town Q. Her average speed for the whole journey was 80 km/h. For the first 1/4 of the journey, she travelled at an average speed of 60 km/h. find her average speed for the remaining journey.

2 x 80 = 160 km (total distance travelled)
160/4 = 40 km (first 1/4 of the journey)
40/60 = 2/3 h (time taken to travel first 1/4 of the journey)
2 – 2/3 = 1 1/3 (time taken to travel the rest, 3/4 of the journey)
(160 – 40) / 1 1/3 = 90

Ans : 90 km/h.

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thank you  so much.

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You are most welcome.

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                               1/4 Journey           3/4 Journey                Total Journey

Ratio of Distance             1                         3                                       4

Actual distance  D           40                     120           <–            80×2=160km

Time=D/S                    40/60=2/3h      4/3 hr        <–                 2hr 

Speed S=D/T                                   120×3/4=90km/h#

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thank you so much. 

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I can’t see all images in all questions and answers… is it only me or…?

Q1 – Ratio method

                              Train    :    Car

Ratio of time         8hrs   :    4 hrs   (1030 to 1830 :  1430 to 1830)

Ratio of speed      1          :        2      (flip ratio for less time, more speed)

Actual speed    60km/h :    120km/h#

Q1 – Speed = Distance x Time

Headstart by Train = 4hours x 60km/h = 240km

Car’s “excess” speed (on top of Train’s 60km/h) must cover 240km shortfall in 4 hrs = 240/4=60km/h

Car’s actual speed = 60+60 = 120km/h#

Q2 – “For the first (?) of the journey” seems like missing something in order to solve. Please check.

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HI SAHMOM, thanks for pointing out my mistake. i had re – post the Qs. thanks.

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