A Car traveling at a constant speed took 1 minute 48 seconds to travel

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

Kindly post all 5 options for this problem

Thanks

Hello alexa,

It is always better to give all answer options with questions otherwise what is the point of OA...Here are few useful posts for navigation on GMATCLUB

all-you-need-for-quant-140445.html#p1130136
rules-for-posting-please-read-this-before-posting-133935.html
best-gmat-math-prep-books-reviews-recommendations-77291.html
_________________

1 Hour = 60 Minutes = 60*60 Seconds = 3600 seconds

We require to convert 108 seconds into hours

\(= \frac{108}{3600} Hours\)

\(Speed = \frac{distance}{time} = 2.4 * \frac{3600}{108} = 80\)

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!

Distance= 2.4 Kms
Time= 1 + 48/60= 1.8/60 hrs

Speed= 2.4 * 60/1.8= 80 km/h
_________________

Where are the options for this question.

\(Speed = \frac{Distance}{Time}\)

We need to find Speed in \(km/hr\), hence convert the units of distance and time in \(kms\) and \(hrs\) respectively.

Given; Distance \(= 2400\) meters \(= 2.4\) kms

Time \(= 1\) minute \(48\) seconds \(= 60 + 48 = 108\) seconds \(= \frac{108}{3600}\) hrs \(= \frac{3}{100}\) hrs

Speed \(= \frac{2.4}{(3/100)} = \frac{2.4*100}{3}\)

Speed \(= \frac{240}{3} = 80\) km/hr

_________________
Please Press "+1 Kudos" to appreciate.

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

If pressed for time, we can estimate:
1min 48s ≈ 2 min
2400/1000 = 2.4 km
1 hr = 60 min --> 60/2 = 30 * 2.4 km = 60+12 = 72 km/hr
Actual km/hr is a bit higher since we rounded up, choose C.

multiply with 18/5 to convert m/s to km/hr

1.48 seconds = 60+48 = 108 seconds

(2400/108)* 18/5 = 80

Option C is the answer

Bunuel I did something similar. Is this the correct way?

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________