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# A students average (arithmetic mean) test score on 4 tests

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Intern
Joined: 08 Nov 2008
Posts: 29
A students average (arithmetic mean) test score on 4 tests  [#permalink]

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11 Nov 2008, 13:33
1
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Difficulty:

5% (low)

Question Stats:

95% (00:30) correct 5% (00:28) wrong based on 152 sessions

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-student-s-average-arithmetic-mean-test-score-on-4-tests-137873.html
SVP
Joined: 30 Apr 2008
Posts: 1840
Location: Oklahoma City
Schools: Hard Knocks

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11 Nov 2008, 13:39
3
E. 88

The student must score at least an 80 for sure. If he scores an 8, then he will need to score 2 pots for each of the 4 other tests to "make up" the difference. They each were at 78 (at least the average is, but this is a small point and doesn't matter to the answer). So 4 tests that were each 2 points short of the 80 average that is desired means the next test must be 8 points higher than the desired average, so 80+8 = 88.

petercao 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

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Manager
Joined: 02 Nov 2009
Posts: 128

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26 Feb 2011, 22:35
1
1
Step 1) Total -= Average* number

total = 78*4 =312

Step 2) T = A*N
4th test + 5th = total
312 +5th test = (80*5)
5th test = 400-312 =88

testing on Total = A*n
Manager
Joined: 18 Jan 2011
Posts: 220

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09 Apr 2011, 15:43
avg on 4 is 78, in order to increase the avg to 80, the new number should be able to contribute 2 to each of the existing 4 numbers i.e. 8 in total so 88.
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Re: A students average (arithmetic mean) test score on 4 tests  [#permalink]

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13 Sep 2013, 08:52
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 $$312+x=400$$ --> $$x=88$$.

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-student-s-average-arithmetic-mean-test-score-on-4-tests-137873.html
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Re: A students average (arithmetic mean) test score on 4 tests  [#permalink]

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21 Jul 2018, 21:02
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A students average (arithmetic mean) test score on 4 tests &nbs [#permalink] 21 Jul 2018, 21:02
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