Lorenzo traveled 120 miles by automobile to visit his brother. The fir

Question

Lorenzo traveled 120 miles by automobile to visit his brother. The first segment of the trip required Lorenzo to drive on 10 miles of city roads before he reached the interstate highway and accelerated to a constant speed of 60 mph. The last segment of the trip was a 10 mile journey over country roads on which Lorenzo averaged 50 miles per hour. If the entire trip took Lorenzo 2 hours and 22 minutes, what was his average speed in miles per hour for the portion of the route between his home and the interstate highway?

A. 15

B. 20

C. 25

D. 30

E. 40

Show Answer

Official Answer

B

A. 15

B. 20

C. 25

D. 30

E. 40

rajatchopra1994 · Answer

Explanation:
Total Distance = 120 miles
Total time = 2 hr 22 mins =   144 mins   Typo Error = 142min  jerryjz2690   ndj5y2  {Edited my typo erro}

Time Taken to cover last segment of trip = 10 /50 = 1/5 hr = 12 mins 
Time taken to cover middle segmentrip of trip = 100 / 60 = 5/3 hr =100 mins
Time Taken to cover first segment of trip =   144    142 - 112 = 30 mins = 1/2hr
Distance of cover in first segment = 10 miles
Speed = 10 / (1/2) = 20

IMO-B

jerryjz2690 · Answer

I used the same process, but I got 144 - 112 = 32 minutes = 32/60 hr
The rate for the first segment is 18.75 mph

Edit: I made a simple arithmetic mistake. It is 142 - 112 = 30 minutes = 1/2 hour

Thank you

Sagart21 · Answer

100 m with 60 mph = 100/60= 1.40hrs
10 miles with 50 mph = 12 mins
Total = 1.52 hrs
2.22-1.52 = 30 mins
10 miles in 30 mins = 20mph

Posted from my mobile device

ndj5y2 · Answer

144-112 is definitely 32. How is the final answer 20?

CrackverbalGMAT · Answer

According to the data in the question, the three sections of the trip starting from the point of journey are of distance 10 miles,100 miles and 10 miles respectively.
The three different speeds in the first, second and third sections are x mph,60 mph and 50 mph respectively.

Starting from the final or last section, time taken to cover it is distance/speed =10/50 =1/5 hrs.
For the second or the middle section, the time taken to cover it is =100/60 =5/3 hrs.
5/3+1/5=28/15 and this is 2/15 less than 30/15 or 2 hrs.
2/15 of an hour =2/15*60= 8 min

As the total time taken is 2hrs 22 min, the first section must have taken 22+8=30 min.
Thus speed for a distance of 10 miles covered in 30min or ½ hour
=distance/time
=10/(1/2) =20 mph (B)

Hope this helps ! Keep studying!

Attachments

File comment: Please refer to the figure for further clarity.

GMAT.jpeg [ 74.66 KiB | Viewed 3271 times ]

ndj5y2 · Answer

Got it there’s a typo 2 hrs 22 min is 142 minutes not 144 minutes

Posted from my mobile device

YogicSpirit · Answer

Now Total Time Given to us = 2 hrs 22 min.
2hrs 22 min in Hrs is = 2 + 22/60 =   71/30 Hrs

let x kmph be the speed for first 10 kms of home to interstate highway

Now, total time = total distance/ speed.

therefore,
71/30 = 10/x + 100/60 + 10/50....

after simplification,
  x=20 kmph.

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.

Lorenzo traveled 120 miles by automobile to visit his brother. The fir

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

Lorenzo traveled 120 miles by automobile to visit his brother. The fir

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