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A student's average (arithmetic mean) test score on 4 tests [#permalink]
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26 Aug 2012, 03:07
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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.



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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A students average (arithmetic mean) test score on 4 tests [#permalink]
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15 Dec 2012, 08:28
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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
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Re: A students average (arithmetic mean) test score on 4 tests [#permalink]
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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).
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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12 Apr 2013, 10:42
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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.



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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19 Jun 2013, 00:56
(8078)=2 2*5tests=10 78+10=88
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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06 Jun 2014, 02:56
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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
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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06 Jun 2014, 06:08
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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!!



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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



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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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.
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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10 Dec 2016, 11:26
Sum(4)=312 Sum(5)=400 Hence the value will be 88
Hence E
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Re: A student's average (arithmetic mean) test score on 4 tests [#permalink]
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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).
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