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A student's average (arithmetic mean) test score on 4 tests [#permalink]
26 Aug 2012, 02:07
1
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Difficulty:
5% (low)
Question Stats:
90% (01:44) correct
10% (00:48) wrong based on 581 sessions
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]
26 Aug 2012, 02:08
Expert's post
SOLUTION:
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]
26 Aug 2012, 07:13
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+
Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
31 Aug 2012, 01:11
Expert's post
SOLUTION:
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]
16 Dec 2012, 03:17
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]
12 Apr 2013, 09:42
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]
06 Jun 2014, 05:08
1
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!!
Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
05 Jul 2014, 07:04
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]
10 Sep 2014, 02:39
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
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