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 Need help on Speed Question
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By: cynqsh66 (offline)  Sunday, April 29 2012 @ 08:25 PM CDT (Read 1043 times)  
cynqsh66

Hello,

Can someone help me with the following question?

Q1. At 3p.m., a regular train left Town A for Town B at an average speed of 75km/h. At 7pm, an express train left Town A for Town B travelling at a constant speed, on parallel path. If the express train took 5Hr to catch up with the regular train, find its average speed.

Q2. Michael and Ron have a bicycle race. Michael cycles at a speed of 48km/h. Ron cycles at a speed of 36km/h. If Michael let Ron start 1h 45mins before him, how long will he take to catch up with Ron?

Thank you very much for helping. Big Grin

cynqsh66

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By: MathIzzzFun (offline)  Sunday, April 29 2012 @ 10:57 PM CDT  
MathIzzzFun

Quote by: cynqsh66

Hello,

Can someone help me with the following question?

Q1. At 3p.m., a regular train left Town A for Town B at an average speed of 75km/h. At 7pm, an express train left Town A for Town B travelling at a constant speed, on parallel path. If the express train took 5Hr to catch up with the regular train, find its average speed.

Q2. Michael and Ron have a bicycle race. Michael cycles at a speed of 48km/h. Ron cycles at a speed of 36km/h. If Michael let Ron start 1h 45mins before him, how long will he take to catch up with Ron?

Thank you very much for helping. Big Grin

cynqsh66



Hi

Use time ratio/speed ratio ..

Q1.
When the express train finally catch up with the regular train,
time taken by express train --> 5h
time taken regular train --> 4h + 5h = 9h
So, express train's speed = 9/5 x 75 km/h = 135 km/h

or use the distance gap to solve ..
At 7pm, distance travelled by regular train = 4 x 75 km = 300 km ie it is 300 km ahead of the express train
since the express train take 5h to catch up, this means that it takes 5h to "make up" the 300km ie it travelled 300 km more than the regular train in 5h or 300/5 = 60km/h faster than the regular train.
So, express train's speed = 75 km/h + 60km/h = 135 km/h

Q2.
speed ratio, Michael : Ron = 48 : 36 = 4 : 3
Time ratio, michael : ron = 3 units : 4 units --> this means that over the same distance michael takes 3 units of time, and ron takes 4 units of time.

1 unit --> 1h 45min, 3 units --> 5h 15 min
Michael will take 5h 15 min to catch up with ron.

cheers.

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By: cynqsh66 (offline)  Sunday, April 29 2012 @ 11:26 PM CDT  
cynqsh66

Hi MathlzzFun,

Thank you again for helping. Big Grin

Best regards
Cynqsh66

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By: hewjt (offline)  Tuesday, May 08 2012 @ 07:48 AM CDT  
hewjt

3pm to 7pm 4h+5h
75kmX9=675km
675km/5=135km

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