Speed/Distance

Expert replies

Previous Topic Next Topic

vaibhav101: Master | Next Rank: 500 Posts; Posts: 138; Joined: Mon May 01, 2017 11:56 pm; Thanked: 4 times

by vaibhav101 » Wed Jun 06, 2018 8:26 am

Timer

00:00

Answers

Stats

Difficulty—

John jogs 9 km at a speed of 6 km/hr. At what speed would she need to jog during the next 1.5 hrs to have an average speed of 9 km/hr for the entire jogging session?

A 9 km/hr
B 10 km/hr
C 12 km/hr
D 14 km/hr
E 15 km/hr

Like this post

Source: Beat The GMAT — Problem Solving | Wed Jun 06, 2018 8:26 am

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8137; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Fri Jun 08, 2018 10:25 am

vaibhav101 wrote:John jogs 9 km at a speed of 6 km/hr. At what speed would she need to jog during the next 1.5 hrs to have an average speed of 9 km/hr for the entire jogging session?

A 9 km/hr
B 10 km/hr
C 12 km/hr
D 14 km/hr
E 15 km/hr

We use the formula: average speed = total distance/total time. We see that John has already jogged 9/6 = 1.5 hours. We can let his new speed be r km/hr for the next 1.5 hours and create the equation:

(9 + 1.5r)/(1.5 + 1.5) = 9

(9 + 1.5r)/3 = 9

9 + 1.5r = 27

1.5r = 18

r = 18/1.5 = 180/15 = 12

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Fri Jun 08, 2018 3:54 pm

Hi vaibhav101,

We're told that John jogs 9 km at a speed of 6 km/hr. We're asked at what speed he would need to jog during the next 1.5 hrs to have an average speed of 9 km/hr for the entire jogging session. This is an example of a Weighted Average question - and since we're given all of the numbers to work with, it really just comes down to doing the necessary Arithmetic.

For the first part of the job, we can use the Distance Formula:
Distance = (Rate)(Time)
9 km = (6 km/hour)(X hours)
9/6 = X
X = 1.5 hours

Since the first 'leg' of the jog was 1.5 hours and the rest of the jog will be 1.5 hours, the TOTAL time for the entire job will be 3 hours. For an average speed of 9 km/hour for the ENTIRE jog, we can use the Average Speed Formula:
Total Distance = (Av. Speed)(Total Time)
Y miles = (9 km/hour)(3 hours)
Y = 27 miles

Since the first leg of the jog covered 9 km, we know that the rest of the job must cover 27 - 9 = 18 miles in 1.5 hours...

Distance = (Rate)(Time)
18 miles = (Z km/hour)(1.5 hours)
18/1.5 = Z
36/3 = Z
Z = 12 km/hour

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review