I travel the first part of my journey at 40 miles per hour and the

Question

I travel the first part of my journey at 40 miles per hour and the second part at 60 miles per hour and cover the total distance of 240 miles to my destination in 5 hours. How long did the first part of my journey last?

A. 4 hours
B. 2 hours
C. 3 hours
D. 2.5 hours
E. 5 hours

A. 4 hours
B. 2 hours
C. 3 hours
D. 2.5 hours
E. 5 hours

CareerGeek · Accepted Answer

Let the time taken for 1st part = t
—> time taken for 2nd part = 5 - t

Total distance = D1 + D2
—> 240 = 40*t + 60*(5 - t)
—> 240 = 40t + 300 - 60t
—> 240 = 300 - 20t
—> 20t = 300 - 240 = 60
—> t = 3 hours

IMO Option C

chetan2u · Answer

Hi,
The question can be done by weighted average method.
The two averages are 40 and 60 and average of entire journey is 240/5=48..
So....40...48....60.
The time for first part will be 5*(60-48)/(60-40)=5*12/20=3

C

Posted from my mobile device

globaldesi · Answer

I tried to solve using allegation method
given average = 48
hence he must have covered the journey in the ratio of 3:2 for 40 kmph to 60 kmph

hence \frac{3}{5}*240 will be distance in first part
divided by avg speed of 40
gives 18/5 as time.

Where did I go wrong?

fireagablast · Answer

Knowns:
Total Distance = 240
Total Time = 5

Equations:
(1) 240 = 5X (where x is the average speed)
(2) 240 = 40t1 + 60t2
(3) 5 = t1+t2

Solve for X:
X = 240/5
X = 48

Combine equations (1), (2), and (3):
5X = 40t1 + 60t2 --------------------(eq 1 and 2)
48(t1+t2) = 40t1 + 60t2 ------------(eq 3;replace 5)

Ratio method:
t1:t2
60-48:48-40
12:8
3:2

t1 = 3
t2 = 2
t1+t2 = 5
240 = 40(3) + 60(2) = 120 + 120 = 240

JohnWidestone · Answer

From my point of view the simplest way is:

I. 60x + 40y = 240
II. x + y = 5

Which has only one solution x = 2 and y = 3 if neither x nor y are equal to 0.

eddyh · Answer

Does the wording of the question vaguely break down the journey was done in equal increments? 120 miles for the first part at 40mph and 120 miles at 60 mph for the second part? 
I got the correct answer approaching it this way after faltering to find a solution using the R * T = D approach as mentioned in this thread.

ScottTargetTestPrep · Answer

We let t = the time to complete the first part of the journey. Thus, (5 - t) = the time to complete the second part of the journey. We can create the distance equation:

40t + 60(5 - t) = 240

40t + 300 - 60t = 240

60 = 20t

3 = t

Answer: C

TheNightKing · Answer

We can use mixtures and allegations.

Average Speed = 240/5 = 48

40 60
 48
12 8

3:2

Well, we know 3 hours at 40 because 3 and 2 add up to 5.

Just to verify 3*40 + 2*60=120+120=240

Note : Even if you can't solve using this method you can just use options and work your way out.

KarishmaB · Answer

Use weighted averages since when averaging speed, the weights are time taken. 
The two speeds are 40 mph and 60 mph and the average speed is 240/5 = 48 mph

w1/w2 = (60 - 48)/(48 = 40) = 3/2

So time taken in the first part of the journey was 3/5th of total time i.e. 3 hrs
Answer (C)

tl169 · Answer

Would it be equally correct to do the weighted average by distance?

Ayeka · Answer

Entire journey = 240 miles
Speed in first half = 40 miles/hour 
Second half= 60 miles
Time taken in first half of journey= t
Time taken in second half= (5-t)

240=40t+60(5-t)
t=3 hrs

Ayeka · Answer

I guess you can, but the calculations will become complex.

bumpbot · Answer

Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.

I travel the first part of my journey at 40 miles per hour and the

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

I travel the first part of my journey at 40 miles per hour and the

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards