Last visit was: 24 Jul 2024, 05:09 It is currently 24 Jul 2024, 05:09
Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
SORT BY:
Date
Math Expert
Joined: 02 Sep 2009
Posts: 94605
Own Kudos [?]: 643493 [4]
Given Kudos: 86734
Send PM
Most Helpful Reply
Math Expert
Joined: 02 Sep 2009
Posts: 94605
Own Kudos [?]: 643493 [6]
Given Kudos: 86734
Send PM
General Discussion
avatar
Intern
Intern
Joined: 16 Aug 2013
Posts: 8
Own Kudos [?]: 4 [0]
Given Kudos: 60
Send PM
avatar
Intern
Intern
Joined: 04 Apr 2014
Posts: 1
Own Kudos [?]: [0]
Given Kudos: 0
Send PM
Re: M13-03 [#permalink]
can you show it substituting ?
Math Expert
Joined: 02 Sep 2009
Posts: 94605
Own Kudos [?]: 643493 [4]
Given Kudos: 86734
Send PM
Re: M13-03 [#permalink]
4
Kudos
Expert Reply
Pakku wrote:
can you show it substituting ?


After taking N tests, each containing 100 questions, John had an average of 70% of correct answers. How much does John need to score on the next test to make his average equal 72%?

A. N−35
B. N+72
C. 2N+70
D. 2N+72
E. 2N−35

Say N=1.

So, after 1 test John has 70 correct answers.
In 2 tests, so in 200 questions he needs to have 0.72*200=144 correct answers, so in the second test he must get 144-70=74 questions correctly.

Now, plug N=1 into the answer choices to see which one yields 74. Only option D fits.

Answer: D.
Intern
Intern
Joined: 22 Jul 2017
Posts: 32
Own Kudos [?]: 22 [1]
Given Kudos: 222
Send PM
Re: M13-03 [#permalink]
1
Bookmarks
Average = Sum / N . Where N is the number of terms

70 = Sum / N "Tests", hence Sum = 70N

72= Sum / N + 1 "Tests"

x= score required on the next test.

Substituting

72= (70N + x) / (N+1)

Solve for X
Math Expert
Joined: 02 Sep 2009
Posts: 94605
Own Kudos [?]: 643493 [0]
Given Kudos: 86734
Send PM
Re: M13-03 [#permalink]
Expert Reply
I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
GMAT Club Bot
Re: M13-03 [#permalink]
Moderators:
Math Expert
94605 posts
Founder
37875 posts