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Percentage/ average [#permalink]
26 Aug 2009, 02:23

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This post received KUDOS

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Difficulty:

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Question Stats:

100% (04:09) correct
0% (00:00) wrong based on 2 sessions

Q. In a class 25% of the students were absent for an exam. 30% failed by 20 marks and 10% just passed because of grace marks of 5. Find the average score of the class if the remaining students scored an average of 60 marks and the pass marks are 33.

1. 37.266 2. 37.6 3. 37.8 4. 36.93 5. 37.5

Pretty easy question but answer given is 37.6 ( considering 75% students when calculating average...i understand 25% are absent...but when average of class is asked shouldnt 100% be included--- pls solve this confusion?)

Re: Percentage/ average [#permalink]
27 Aug 2009, 05:12

Economist wrote:

Ans should be 27.7 !! Anything missing?

Hi buddy, asuming that question is ok, how did you get to your 27.7? I have a totally different nbr

Assuming it is a class of 200 students. 50 were absent, and 150 were at the exam. 30% failed by 20 marks => means 45 students scored 13 10% just passed with a 5mark grant => means 15 students scored 28 the rest scored 60 => 90 students

Re: Percentage/ average [#permalink]
27 Aug 2009, 05:42

defoue wrote:

Economist wrote:

Ans should be 27.7 !! Anything missing?

Hi buddy, asuming that question is ok, how did you get to your 27.7? I have a totally different nbr

Assuming it is a class of 200 students. 50 were absent, and 150 were at the exam. 30% failed by 20 marks => means 45 students scored 13 10% just passed with a 5mark grant => means 15 students scored 28 the rest scored 60 => 90 students

avg = {(45x13)+(15x28)+(90x60)}/200 = 32.025

am I doing something wrong here?

Thx for your feedback

Actually it is a poorly worded question. I took 30% of overall students, you have taken 30% of passed students and so on...that is why we are getting different answers. Logically yes, absent students are to be discounted but the question does not specify anything. It is also possible that 30% of overall failed

Re: Percentage/ average [#permalink]
27 Aug 2009, 08:22

rohansherry wrote:

guess the ques is right ..IMO B

say 100 students are in class

75 appeared for test. 33 is passing mark

30 students got 13 marks each and failed by 20 marks - their total marks = 390

10 got 28 marks each and just passed by 5 grace - their total marks = 280 (excluding grace marks)

remaining 35 got 60 on average - their total marks = 2100

total marks secured by all 75 who appeared in test = 390+280+2100 = 2770

avg marks = 2770/75 = 36.93

-->note that if grace marks are included for 10 just passed students then

their total = 330

final total = 2820

avg marks = 2820/75 = 37.6

Please correct if I'm wrong.

So it means grace marks have to be included

I comletely agree with this solution. No one says that absent students fail the course and should be given 0. But it is a tricky one. Kudo for you. If you do not include 25% that were abscent you get the following: 40%X13+13.33%X28+46.66%X60=36.93

However, answer is D. They say "remaining"...so overlap is not possible

Re: Percentage/ average [#permalink]
28 Aug 2009, 01:43

rohansherry wrote:

guess the ques is right ..IMO B

say 100 students are in class

75 appeared for test. 33 is passing mark

30 students got 13 marks each and failed by 20 marks - their total marks = 390

10 got 28 marks each and just passed by 5 grace - their total marks = 280 (excluding grace marks)

remaining 35 got 60 on average - their total marks = 2100

total marks secured by all 75 who appeared in test = 390+280+2100 = 2770

avg marks = 2770/75 = 36.93

-->note that if grace marks are included for 10 just passed students then

their total = 330

final total = 2820

avg marks = 2820/75 = 37.6

Please correct if I'm wrong.

So it means grace marks have to be included

Why did you assume that all 10 students got 28? If the grace mark is 5, I understand that they could get min 28 marks. Is it possible the student got 30 marks and passed due to grace mark is 5? Correct me if i'm wrong

Re: Percentage/ average [#permalink]
28 Aug 2009, 02:44

defoue wrote:

Economist wrote:

Ans should be 27.7 !! Anything missing?

Hi buddy, asuming that question is ok, how did you get to your 27.7? I have a totally different nbr

Assuming it is a class of 200 students. 50 were absent, and 150 were at the exam. 30% failed by 20 marks => means 45 students scored 13 10% just passed with a 5mark grant => means 15 students scored 28 the rest scored 60 => 90 students

avg = {(45x13)+(15x28)+(90x60)}/200 = 32.025

am I doing something wrong here?

Thx for your feedback

I guess you need to include the grace marks also(anyway this marks also comes into the account). Assuming total 200 students 30% = 45*13 = 585 10% = 15*33 = 495 60% = 90*60 = 5400 =32.2

/Prabu

gmatclubot

Re: Percentage/ average
[#permalink]
28 Aug 2009, 02:44