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

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A students average (arithmetic mean) test score on 4 tests [#permalink] New post 11 Nov 2008, 12:33
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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
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Re: student's score [#permalink] New post 11 Nov 2008, 12:39
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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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Re: student's score [#permalink] New post 26 Feb 2011, 21:35
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
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Re: student's score [#permalink] New post 09 Apr 2011, 14:43
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] New post 13 Sep 2013, 06:52
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Re: A students average (arithmetic mean) test score on 4 tests [#permalink] New post 13 Sep 2013, 07:52
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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

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.

Answer: E.

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] 13 Sep 2013, 07:52
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