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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

93% (00:41) correct
7% (00:41) wrong based on 1278 sessions

HideShow timer Statistics

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

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.

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!!

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

Since the student's average test score on 4 tests is 78, then the sum of the first 4 test scores is 4*78=312. We need the sum of ALL 5 scores to be 5*80=400, so if \(x\) is the 5th test score, then \(312+x=400\) --> \(x=88\).

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 succeed--Michael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+

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

Since the student's average test score on 4 tests is 78, then the sum of the first 4 test scores is 4*78=312. We need the sum of ALL 5 scores to be 5*80=400, so if \(x\) is the 5th test score, then \(312+x=400\) --> \(x=88\).

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).
_________________

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

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.

400-312=88.

so in the fifth test the score should be 88 for the mean to become 80

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 Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions

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+

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