For today's training session, a cyclist rode 50 kilometers on a bike

Question

For today's training session, a cyclist rode 50 kilometers on a bike trail at an average speed of 40 kilometers per hour and returned on the same trail at an average speed of 20 kilometers per hour. Which of the following is closest to the cyclist's average speed for the training session, in kilometers per hour?

A. 24
B. 27
C. 30
D. 33
E. 36

Solution:
First side time taken =
total Distance=100
Total Time Taken= 50/40+50/20
= 1.25 hrs+2.5 hrs
=3.75 hrs
=3 hrs 45 mins
=100/3.75
=100*4/15
=26.66

A. 24
B. 27
C. 30
D. 33
E. 36

JeffTargetTestPrep · Accepted Answer

There:

distance = 50 km
rate = 40 km/h
time = distance/rate = 50/40 = 5/4 hours

Back:

distance = 50 km
rate = 20 km/h
time = distance/rate = 50/20 = 5/2 hours

Today’s session:

total distance = 50 + 50 = 100 km
total time = 5/4 + 5/2 = 15/4 hours

average speed = total distance/total time
average speed = 100/(15/4) = 100(4/15) = 80/3 ≈ 27 km/h

Answer: B

gmatophobia · Answer

Average Speed = Total Distance Travelled / Total Time Taken

Total Time =  \frac{50}{40} + \frac{50}{20} = \frac{150}{40} = \frac{15}{4}

Total Distance = 50*2 = 100

Average Speed =  \frac{100*4}{15}

15 * 6 = 90

15 * 7 = 105

100 is closer to 105, therefore

Average Speed  \approx  7*4 = 28. The value in Option B is the closest.

Option B

RushilVasudev · Answer

avg speed = 2 * S1*S2/S1+S2 
=> 2 * 40*20/60
=> 27

Paras96 · Answer

Average speed when the distance is same = 2s1s2/(s1+s2)

where s1 and s2 are the speed with same distance travelled

therefore 
=> 2*40*20/60= 26.677 kmph hence B

harshittahuja · Answer

For today's training session, a cyclist rode 50 kilometers on a bike trail at an average speed of 40 kilometers per hour and returned on the same trail at an average speed of 20 kilometers per hour. Which of the following is closest to the cyclist's average speed for the training session, in kilometers per hour?

A. 24
B. 27
C. 30
D. 33
E. 36

Solution:
First side time taken =
total Distance=100
Total Time Taken= 50/40+50/20
= 1.25 hrs+2.5 hrs
=3.75 hrs
=3 hrs 45 mins
=100/3.75
=100*4/15
=26.66

A. 24
B. 27
C. 30
D. 33
E. 36

Solution:
First side time taken =
total Distance=100
Total Time Taken= 50/40+50/20
= 1.25 hrs+2.5 hrs
=3.75 hrs
=3 hrs 45 mins
=100/3.75
=100*4/15
=26.66

CrackverbalGMAT · Answer

Hi! Lets solve this question in three steps, with focus on logic and critical thinking. 1: Smart Assumption of Distance Since the problem involves a return journey on the same trail, the distance for each lap remains constant.

Here's a critical thinking tip: instead of sticking to the given distance (50 km), assume a smart value for distance that simplifies our calculations. Since the distances covered in the two trails are equal, choose 40 km as the distance for each trail, the least common multiple of 20 and 40 km/h(the speeds for each lap).This way, you avoid fractions and deal with integers for time, making the calculation easier. 2: Calculate Time for Each Lap For the first lap at 40 km/h, the time taken would be \frac{40km}{40kmph } = 1 hour For the return lap at 20 km/h, the time would be \frac{40km}{ 20kmph } = 2hours 3: Computing Average Speed Remember, average speed is calculated as Total Distance Covered divided by Total Time Taken. Here, the journey has two laps of 40 km each. So, the average speed = \frac{(40km + 40km) }{(1 hour+2hours)} =80km/3hours ≈27 km/h This matches option B. Devmitra Sen Head of Academics,Crackverbal Connect with me on LinkedIn

hemanthPA · Answer

https://gmatclub.com/forum/download/file.php?id=83233 GMAT-Club-Forum-vml8d1rp.png

RishiS01 · Answer

Hi, quick question: Why can't we just average the speeds. Clearly we get an incorrect answer when we do that but that was my intuition when I first saw the q on the test and I'm wondering when and where I can actually do that vs not.

GMATinsight · Answer

Average Speed = Total Distance / Total Time

Average Speed = (50+50) /   = 100*40 / 50*(3) = 80/3 = 26.66 ≈ 27

Answer: Option B

Related Video:
  https://www.youtube.com/watch?v=7fDq4J7-pho

GMATinsight · Answer

RishiS01

We can average the speed when the speed is constantly increasing or constantly decreasing. (Case 2)

Here the case is constant speed of 40 while going forward and constant speed of 20 while coming backwards (Case 1)

RishiS01 · Answer

This visual helps a lot, thanks!!

For today's training session, a cyclist rode 50 kilometers on a bike

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

For today's training session, a cyclist rode 50 kilometers on a bike

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