Answer required in Km/Hr

Distance = 2400 Meters = \(\frac{2400}{1000}\) Kms = 2.4 Kilometers

Time = 1 Minute 48 Seconds = 60+48 = 108 seconds = \(\frac{108}{60}\) Minutes = \(\frac{108}{60*60}\) Hours

Speed \(= \frac{2.4}{\frac{108}{60*60}} = 0.8 * 10 * 10 = 80\)

Answer = 80
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Hello alexa,

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I arrived to the correct answer (80), but it took me quite long.

I have trouble converting units.

I did 1hr = 60min, and 60 min = 60 sec per min. So, 60x60 = 3,600 seconds in 1 hour.

So 108 seconds / 3,600 to convert to hours (this is the messy part, as then I divided 108/3,600 to get 0.031 hours).

Finally did 2.4 / 0.031 as 240 / 3 to get 80.

Any tips so that I can convert units and make the process easier and less prone to mistakes?

Thanks!

Where are the options for this question.
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Whenever, we need to convert a speed in km/hr to m/s, you multiply it by a factor of \(\frac{5}{18}\)
We arrive to \(\frac{5}{18}\) as follows :

1 km is 1000 meters
1 hr is 60 minute, and 1 minute is 60 seconds.
1 hr is 3600 seconds

So 1 km/hr essentially converts to \(\frac{1000}{3600}\) or \(\frac{5}{18}\)m/s
Therefore, In order to convert the speed from m/s to km/hr, you must multiply it by a factor of \(\frac{18}{5}\)

Coming back to the question in hand
The car travels 2400 meters in 1 minute 48 seconds(108 seconds)
Speed(in m/s) = \(\frac{Distance}{Time} = \frac{2400}{108} = \frac{200}{9}\)

In order to convert the speed in the format that it has been asked in, we multiply it by a factor of \(\frac{18}{5}\)

So, the converted speed(in km/hour as asked in the question) is \(\frac{200}{9}*\frac{18}{5}\) = 80 km/hr.

Hi Bunuel,
Can you please add options to this question to make it more GMAT-like!
Thanks
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Quickest method:

Work backward as the answer choices looks good and far appart.

Test B - 60 km/h = 60km/60min so 1km/min. The time necessary to do 2.4km = 2.4 min. Our car is FASTER as it does it in 1 min 48s ==> ELIMINATE A AND B.

Test D - 90 km/h = 90km/60min so 3km/2min so 1.5 km/min. The time necessary to do 2.4km = 2.4/1.5 = 24/15 = 1.6 min = 96 seconds. Our car is going SLOWER as it does it in 60 sec + 48 sec = 108 sec ==> ELIMINATE D AND E.

You are then left with answer C.