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convertions 80km/hr - meters/second

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convertions 80km/hr - meters/second

by cgc » Wed Jan 13, 2010 9:29 am
It is not terribly difficult but I find myself taking too long to answer this question. How would you approach this question to answer it fast?

How many seconds will it take for a bus that is traveling at a constant rate of 80 kilometers per hour to travel a distance of 400 meters? (1km = 1000 meters)

(a) 5
(b) 12
(c) 18
(d) 20
(e) 30

Cheers,
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by truplayer256 » Wed Jan 13, 2010 10:07 am
80 kilometers means 80*1000=80000 m. The bus can travel 80000m in 3600 seconds which means that it can travel 400 kilometers in 3600/200 or 18 seconds.
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by cgc » Wed Jan 13, 2010 12:20 pm
ok so converting it from km/hr to meters/sec makes sense!!

80km/1hour * 1000meters/60min*60sec
= 8000meters/3,600sec

However, should the question be 80,000 meters or 800 km instead to get the answer of 400km/18 seconds?????

400meters/18seconds
=200(400/18)
=80,000meters/3,600seconds

Did I miss something???
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by cgc » Wed Jan 13, 2010 12:21 pm
sorry above should be 400 meters/18 seconds (4th line)
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by Brent@GMATPrepNow » Wed Jan 13, 2010 12:31 pm
cgc wrote:It is not terribly difficult but I find myself taking too long to answer this question. How would you approach this question to answer it fast?

How many seconds will it take for a bus that is traveling at a constant rate of 80 kilometers per hour to travel a distance of 400 meters? (1km = 1000 meters)

(a) 5
(b) 12
(c) 18
(d) 20
(e) 30

Cheers,
Here's an approach you can pretty much do in your head.
First recognize that 80 km = 80,000 m, so the bus travels 80,000 meters per hour.
We can see a relationship between 80,000 and 400
In your head, you might begin by seeing that, in 1/2 an hour, the bus would travel 40,000m (we now have the "4" part, but we want 400m not 40,000m)
From here we can see that, in 1/20 of an hour, the bus would travel 4,000m (closer)
So, in 1/200 of an hour, the bus would travel 400m --> great, the answer is 1/200 of an hour (almost done).

Convert 1/200 hours to seconds.
Since 1 hour = 3600 seconds, we want 1/200 of 3600, which equals 18.
Brent Hanneson - Creator of GMATPrepNow.com
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