GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 05 Dec 2019, 10:02

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Steven has run a certain number of laps around a track at an average (

Author Message
TAGS:

### Hide Tags

Senior RC Moderator
Joined: 02 Nov 2016
Posts: 4554
GPA: 3.39
Steven has run a certain number of laps around a track at an average (  [#permalink]

### Show Tags

14 Feb 2019, 02:31
1
00:00

Difficulty:

25% (medium)

Question Stats:

85% (01:38) correct 15% (02:26) wrong based on 27 sessions

### HideShow timer Statistics

Steven has run a certain number of laps around a track at an average (arithmetic mean) time per lap of 51 seconds. If he runs one additional lap in 39 seconds and reduces his average time per lap to 49 seconds, how many laps did he run at an average time per lap of 51 seconds?

A. 2
B. 5
C. 6
D. 10
E. 12

_________________
CEO
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2977
Location: India
GMAT: INSIGHT
Schools: Darden '21
WE: Education (Education)
Re: Steven has run a certain number of laps around a track at an average (  [#permalink]

### Show Tags

14 Feb 2019, 04:29
Steven has run a certain number of laps around a track at an average (arithmetic mean) time per lap of 51 seconds. If he runs one additional lap in 39 seconds and reduces his average time per lap to 49 seconds, how many laps did he run at an average time per lap of 51 seconds?

A. 2
B. 5
C. 6
D. 10
E. 12

Total Time = 51*x for x laps

Total time after one more lap = 51x + 39

Average time now = (51x + 39) / (x+1) = 49

i.e. x = 5

_________________
Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9848
Location: Pune, India
Re: Steven has run a certain number of laps around a track at an average (  [#permalink]

### Show Tags

14 Feb 2019, 05:58
Steven has run a certain number of laps around a track at an average (arithmetic mean) time per lap of 51 seconds. If he runs one additional lap in 39 seconds and reduces his average time per lap to 49 seconds, how many laps did he run at an average time per lap of 51 seconds?

A. 2
B. 5
C. 6
D. 10
E. 12

Average = 51 secs
One additional lap time = 39 secs, which reduces average by 2 secs (from 51 secs to 49 secs).
So the -12 secs (39 is 12 less than 51) from the average is distributed among 6 laps to give -2 to each)

So there must have been 5 laps at the average of 51 secs.

This method is discussed in detail here: https://www.veritasprep.com/blog/2012/0 ... etic-mean/
_________________
Karishma
Veritas Prep GMAT Instructor

GMAT Club Legend
Joined: 18 Aug 2017
Posts: 5428
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: Steven has run a certain number of laps around a track at an average (  [#permalink]

### Show Tags

14 Feb 2019, 09:39
Steven has run a certain number of laps around a track at an average (arithmetic mean) time per lap of 51 seconds. If he runs one additional lap in 39 seconds and reduces his average time per lap to 49 seconds, how many laps did he run at an average time per lap of 51 seconds?

A. 2
B. 5
C. 6
D. 10
E. 12

given
sum of laps / total laps = 51

now
sum of laps + 39 / total laps + 1 = 49

so
we can say sum of laps = 51 * total laps

so
51 * total laps + 39 = 49 * total laps + 49
total laps = 10/2 ~ 5
IMO B
Re: Steven has run a certain number of laps around a track at an average (   [#permalink] 14 Feb 2019, 09:39
Display posts from previous: Sort by