'Distance/Speed/Time' Word Problems Made Easy

amsood · **Posted:** Wed Dec 15, 2010 1:06 pm

Good one. Much appreciated.

puneetj · **Posted:** Sun Jan 02, 2011 7:15 pm

The tabular form is very useful. Great Job!!

dgupt6 · **Posted:** Sat Jan 15, 2011 12:02 pm

This tabular techique is good.

menacel · **Posted:** Sat Mar 19, 2011 11:18 am

thanks this and your other posts break the concepts down so much better for me than the MGMAT books!

tparanidharan · **Posted:** Wed Apr 27, 2011 12:33 pm

this post really made me to solve D*S*T problems like a cake walk..thankssssss

dkj1984 · **Posted:** Mon Jul 25, 2011 8:24 am

Example 2.
An executive drove from home at an average speed of 30 mph to an airport where a helicopter was waiting. The executive boarded the helicopter and flew to the corporate offices at an average speed of 60 mph. The entire distance was 150 miles; the entire trip took three hours. Find the distance from the airport to the corporate offices.

Hi ,

Can someone please let me know what would be the average sped in this case .

Will it be total distance / total time = 150 / 3 or will it be 2ab/a+b = 2(30*60) / 90

Please advise.

Thanks!

Regards,
Divya

dkj1984 · **Posted:** Thu Jul 28, 2011 10:32 am

Thanks a lot Karishma!

you always put in weighted average approaches and make them look so simple !

Thanks for pointing the part I had overlooked.

Regards,

VeritasPrepKarishma · **Posted:** Thu Jul 28, 2011 8:59 pm

dkj1984 wrote:

Thanks a lot Karishma!

you always put in weighted average approaches and make them look so simple !

Thanks for pointing the part I had overlooked.

Regards,

That is because weighted averages has applications in almost all topics of Arithmetic. That is the reason I keep insisting that you should be comfortable with this topic. It makes many other topics simpler.

krishp84 · **Posted:** Sat Jul 30, 2011 9:42 pm

yups - weighted average is a great approach to solve this problem.
+1 Kudos

devinawilliam83 · **Posted:** Wed Oct 19, 2011 5:36 am

This is superb stuff. Thanks so much for sharing this

mismary207 · **Posted:** Mon Nov 28, 2011 1:38 am

Hi,

Thanks very much for this comment. It help me to think about my ideals.

Tks again and pls keep posting.

Jdam · **Posted:** Fri Dec 02, 2011 6:50 pm

great job. thanks!

Thanu1083 · **Posted:** Wed Jan 25, 2012 7:33 am

sriharimurthy wrote:

macsin wrote:

Guys any luck with the images please? I am not able to view them Solution 2 onwards.

Hi,
Not quite sure what the problem might be.. I'm able to view the images. Anyone else facing this problem?

I am not able to view images from image 2. Please help.

Bunuel · **Posted:** Wed Jan 25, 2012 8:34 am

Thanu1083 wrote:

sriharimurthy wrote:

macsin wrote:

Guys any luck with the images please? I am not able to view them Solution 2 onwards.

Hi,
Not quite sure what the problem might be.. I'm able to view the images. Anyone else facing this problem?

I am not able to view images from image 2. Please help.

Welcome to GMAT Club,

Someone on the forum noted that it might be because of the browser (some versions of IE). Try Firefox or Google Chrome. Or just try to reloading a page several times... Maybe it was just one time error.

Hope it helps.

Yekrut · **Posted:** Wed Feb 29, 2012 3:58 pm

Thank you for the great questions. I really felt like I was starting to get the hang of it at the end. It's good to have the same type of questions grouped together, helps with my practice.

budablasta · **Posted:** Thu Mar 08, 2012 6:57 am

Thank you so much for this breathtakingly lucid take on DST!

jty107 · **Posted:** Tue Mar 27, 2012 11:32 am

Awesome post! Thanks.

Galiya · **Posted:** Thu Apr 12, 2012 1:28 am

Quote:

Example 1.
To qualify for a race, you need to average 60 mph driving two laps around a 1-mile long track. You have some sort of engine difficulty the first lap so that you only average 30 mph during that lap; how fast do you have to drive the second lap to average 60 for both of them?

...

Quote:

Now, we know that the total time should be the sum of the times in row 1 and 2. Thus we can form the following equation :

Time(3) = Time(1) + Time(2) ---> 1/30 = 1/30 + 1/x

From this, it becomes clear that '1/x' must be 0.

Since 'x' is the reciprocal of 0, which does not exist, there can be no speed for which the average can be made up in the second lap.

why can't i use w.averages formula here?

(30*1+X*1)/2=60 --> (30*1+X*1)=120 --> X=90 mph one needs to drive to average 60 mph after 2 laps

VeritasPrepKarishma · **Posted:** Thu Apr 12, 2012 6:11 am

Galiya wrote:

Quote:

Example 1.
To qualify for a race, you need to average 60 mph driving two laps around a 1-mile long track. You have some sort of engine difficulty the first lap so that you only average 30 mph during that lap; how fast do you have to drive the second lap to average 60 for both of them?

...
why can't i use w.averages formula here?

(30*1+X*1)/2=60 --> (30*1+X*1)=120 --> X=90 mph one needs to drive to average 60 mph after 2 laps

Because in weighted average formula, the weights (w1 and w2) will be the time traveled, not the distance traveled.

Average Speed = Total Distance/Total Time

Average Speed = (Speed1*Time1 + Speed2*Time2)/(Time1 + Time2) (This is your weighted average formula)

What you are doing above is Average Speed = (Speed1*Distance1 + Speed2*Distance2)/(Distance1 + Distance2) which is incorrect.

Check out these two additional links to figure out how to know what weights to use:

a-certain-car-traveled-twice-as-many-miles-from-town-a-127918.html?hilit=average%20speed%20time
if-a-car-traveled-from-townsend-to-smallville-at-an-average-122843.html?hilit=average%20speed%20time

jsphcal · **Posted:** Sat Apr 28, 2012 11:42 am

Now if speed of the current is 3 mph, then the speed of the boat while going downstream and upstream will be 'b + 3' and 'b - 3' respectively.

could you please elaborate more on the + 3 and -3 respectively?

instead of upstream and downstream we could have used with current and against current?

Great post!!

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'Distance/Speed/Time' Word Problems Made Easy

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