Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 44290

A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
26 Aug 2012, 03:07
1
This post received KUDOS
Expert's post
3
This post was BOOKMARKED
Question Stats:
93% (00:41) correct 7% (00:43) wrong based on 1413 sessions
HideShow timer Statistics



Math Expert
Joined: 02 Sep 2009
Posts: 44290

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
26 Aug 2012, 03:08
2
This post received KUDOS
Expert's post
2
This post was BOOKMARKED



Manager
Status: Prevent and prepare. Not repent and repair!!
Joined: 13 Feb 2010
Posts: 242
Location: India
Concentration: Technology, General Management
GPA: 3.75
WE: Sales (Telecommunications)

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
26 Aug 2012, 08:13
Let the score in the 5th test be x. The sum of the first 4 tests = 78*4=312 Now it implies 312+x/5=80 Therefore x=88
_________________
I've failed over and over and over again in my life and that is why I succeedMichael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+



Intern
Joined: 21 Apr 2010
Posts: 11

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
27 Aug 2012, 11:15
(sum of x)/4 = 78 So (sum of x) = 312. Now (sum of x + x5)/5=80 So (312+x5)=400 i.e. x5=88.



Manager
Joined: 13 Feb 2012
Posts: 141
Location: Italy
Concentration: General Management, Entrepreneurship
GPA: 3.1
WE: Sales (Transportation)

A students average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
15 Dec 2012, 08:28
1
This post received KUDOS
I follow Manhattan advice on this one and write the average formula as a first thing: in order to reach an average of 80 over 5 test the students has to reach 400 points; he now has 78*4= 312. 400312= 88. Answer E
_________________
"The Burnout"  My Debrief
Kudos if I helped you
Andy



Intern
Joined: 24 Apr 2012
Posts: 48

Re: A students average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
16 Dec 2012, 04:17
Ans: total score after 4 tests=312 and score needed after 5 tests= 5x80=400 the student scores the difference in the 5th test which is 88 , (E).
_________________
www.mnemoniceducation.com
TURN ON YOUR MINDS!!!



Intern
Joined: 04 Apr 2013
Posts: 31

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
12 Apr 2013, 10:42
5
This post received KUDOS
Examining the known average can simply things. We need to reach 80. We currently have 78, four times. 78 is 2 away from 80. Having this four times weights our average 8 off what is desires. To 'catch up' to the average in one test, we must make up the full 8 point deficit in one test. We need an 88. 88  8 = 80.



Senior Manager
Joined: 23 Oct 2010
Posts: 370
Location: Azerbaijan
Concentration: Finance

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
19 Jun 2013, 00:56
(8078)=2 2*5tests=10 78+10=88
_________________
Happy are those who dream dreams and are ready to pay the price to make them come true
I am still on all gmat forums. msg me if you want to ask me smth



SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1838
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
06 Jun 2014, 02:56
5
This post received KUDOS
Let students score be 78..... 78..... 78....... 78 Average after 5th test should be 80 So score in 5th exam should at least be 80 & also it should "cover up the loses" in the earlier tests Loses earlier = 2 per test = 2 * 4 = 8 80 + 8 = 88 Answer = E
_________________
Kindly press "+1 Kudos" to appreciate



Manager
Joined: 15 Aug 2013
Posts: 58

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
06 Jun 2014, 06:08
3
This post received KUDOS
I will suggest a little different solution (not a very great trick) but very useful for finding averages since it can save your "TIME" at the tests... Average of 5 tests to be 80 suggests  in each test the student scored 80 (and this can make average 80). SO  In 5th test the student has to score 80 for sure, plus any deficit to make up for the average. We know in 4 tests his averge was 78, which means he is 2 markes short of average(80 in this case) in previous 4 tests and he has to make up for this deficit in the 5th test. Hence he has to score 2 * 4 (deficit * no of tests) = 8. Remember, he has to score 80 also in the 5th test. Hence in total  80 + 8 = 88. Choice E
Here is how I would approach  80 in the 5th test, and 2 *4 = 8 totl 88 n the 5th tests. SO it took few seconds to do the ques... Practise this kind of technique while solving questions n averages has been very handy for m... All the best!!



Intern
Joined: 05 Jul 2014
Posts: 1

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
05 Jul 2014, 08:04
zerosleep wrote: I will suggest a little different solution (not a very great trick) but very useful for finding averages since it can save your "TIME" at the tests... Average of 5 tests to be 80 suggests  in each test the student scored 80 (and this can make average 80). SO  In 5th test the student has to score 80 for sure, plus any deficit to make up for the average. We know in 4 tests his averge was 78, which means he is 2 markes short of average(80 in this case) in previous 4 tests and he has to make up for this deficit in the 5th test. Hence he has to score 2 * 4 (deficit * no of tests) = 8. Remember, he has to score 80 also in the 5th test. Hence in total  80 + 8 = 88. Choice E
Here is how I would approach  80 in the 5th test, and 2 *4 = 8 totl 88 n the 5th tests. SO it took few seconds to do the ques... Practise this kind of technique while solving questions n averages has been very handy for m... All the best!! Thanks zerosleep.. I always followed traditional approach.. now i would try your way when encountered with question on averages



Manager
Joined: 07 Apr 2014
Posts: 130

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
10 Sep 2014, 03:39
Bunuel wrote: A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80? (A) 80 (B) 82 (C) 84 (D) 86 (E) 88 Practice Questions Question: 30 Page: 156 Difficulty: 600 total of 4 test = 4*78 = 312 if the mean of 5 test has to be 80 then total has to be 400. 400312=88. so in the fifth test the score should be 88 for the mean to become 80



Intern
Joined: 06 Nov 2014
Posts: 12

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
16 Nov 2014, 08:40
(4*78+x)/5=80 x=(5*80)(4*78) ok so 5*784*78= 78, x= 5*(8078) + 78 > 5*2+78 total score required 78+10=88



Retired Moderator
Joined: 23 Sep 2015
Posts: 401
Location: France
GMAT 1: 690 Q47 V38 GMAT 2: 700 Q48 V38
WE: Real Estate (Mutual Funds and Brokerage)

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
23 Nov 2015, 11:51
Alternative approach : (New data  Old avg)/New number of items in the set = change in average (New  78) /5 = 2 New = 88
_________________
New Application Tracker : update your school profiles instantly!



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2116

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
25 May 2016, 07:18
Bunuel wrote: A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?
(A) 80 (B) 82 (C) 84 (D) 86 (E) 88 To solve, we use the average equation: average = sum/quantity We don't know the individual scores for each of the first 4 tests, but because their average is 78, we can think of the first 4 scores as 4 scores of 78 each. We then multiply 78 by 4 to get the sum of those four tests: 78 x 4 = 312 Let's let n = the score on the 5th test. Thus, the sum of the 5 tests is 312 + 5th test score, or 312 + n. Also, because the new average will be 80, we substitute 80 for the new average. We can now solve for n. Average = sum/quantity 80 = (312 + n)/5 400 = 312 + n 88 = n The answer is E.
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Current Student
Joined: 18 Oct 2014
Posts: 901
Location: United States
GPA: 3.98

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
25 May 2016, 08:46
Bunuel wrote: A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80? (A) 80 (B) 82 (C) 84 (D) 86 (E) 88 Practice Questions Question: 30 Page: 156 Difficulty: 600 To have avg score of 80 implies that student needs 80 marks in all 5 tests. That means 2 marks increase in all 4 tests= 4*2= 8 total marks increase in 4 tests + 80 marks in 5th tests= 88 marks E is the answer
_________________
I welcome critical analysis of my post!! That will help me reach 700+



BSchool Forum Moderator
Joined: 12 Aug 2015
Posts: 2493
GRE 1: 323 Q169 V154

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
10 Dec 2016, 11:26



Director
Joined: 02 Sep 2016
Posts: 777

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
01 Apr 2017, 09:12
Total score in 4 tests= 4*78=312 The average of 5 tests is 80. Therefore the total score of 5 tests= 5*80=400 Therefore in the 5th test, the student must score 88 (400312).
_________________
Help me make my explanation better by providing a logical feedback.
If you liked the post, HIT KUDOS !!
Don't quit.............Do it.



Manager
Joined: 07 Jun 2017
Posts: 176
Location: India
Concentration: Technology, General Management
GPA: 3.6
WE: Information Technology (Computer Software)

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
14 Sep 2017, 00:16
average is 78 from 4 tests required average is 80 2*4 need to be covered from the 5th test so 80+8 = 88 he should get So answer is E
_________________
Regards, Naveen email: nkmungila@gmail.com Please press kudos if you like this post



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11255
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
Show Tags
29 Jan 2018, 16:02
Hi All, The standard average formula 'approach' is likely the easiest for most Test Takers to use on these types of prompts. However, there is another way to think about this prompt  since the average of the first 4 tests is 78, we can think of those tests as four 78s. For a 5th exam to raise the overall average to 80, that exam has to score 80 points on its own AND raise each of the other 4 tests to 80. Those 4 tests would require an extra 2 points apiece... 80 + 4(2) = 88 points Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************




Re: A student's average (arithmetic mean) test score on 4 tests
[#permalink]
29 Jan 2018, 16:02






