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# A student took 12 tests. The student's average (arithmetic mean) on

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Senior Manager
Status: Gathering chakra
Joined: 05 Feb 2018
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A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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Updated on: 25 Apr 2019, 20:43
3
00:00

Difficulty:

75% (hard)

Question Stats:

70% (01:32) correct 30% (02:21) wrong based on 30 sessions

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A student took 12 tests. The student's average (arithmetic mean) on the first 4 tests was of the student's average score on the final 8 tests. What fraction of the total number of points that the student scored on all 12 tests was the total number of points that the student scored on the first 4 tests?

A) $$\frac{3}{20}$$

B) $$\frac{1}{4}$$

C) $$\frac{3}{10}$$

D) $$\frac{1}{3}$$

E) $$\frac{3}{8}$$

Originally posted by energetics on 26 Mar 2019, 11:51.
Last edited by energetics on 25 Apr 2019, 20:43, edited 1 time in total.
Intern
Joined: 18 Jan 2019
Posts: 28
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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31 Mar 2019, 02:33
energetics wrote:
A student took 12 tests. The student's average (arithmetic mean) on the first 4 tests was of the student's average score on the final 8 tests. What fraction of the total number of points that the student scored on all 12 tests was the total number of points that the student scored on the first 4 tests?

A) $$\frac{3}{20}$$

B) $$\frac{1}{4}$$

C) $$\frac{3}{10}$$

D) $$\frac{1}{3}$$

E) $$\frac{3}{8}$$

can someone explain this please, i get 1/4
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Joined: 25 Feb 2019
Posts: 280
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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31 Mar 2019, 02:57
1
IMO D.

Mean of first four tests = mean of final 8 tests = x

marks scored in first 4 tests = 4x

marks in final 8 tests = 8x

total marks = 12x

so in fraction = 4x/12x
= 1/3

Posted from my mobile device
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Joined: 18 Jan 2019
Posts: 28
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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31 Mar 2019, 03:19
m1033512 wrote:
IMO D.

Mean of first four tests = mean of final 8 tests = x

marks scored in first 4 tests = 4x

marks in final 8 tests = 8x

total marks = 12x

so in fraction = 4x/12x
= 1/3

Posted from my mobile device

I did:

average of first 4: x/4

average of last 8: y/8

from question: x/4=y/8 ---> y=2x

average of all 12 Qs: (x+y)/12

sub y=2x--->(2x+x)/12---> 3x/12---->1/4 x
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Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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31 Mar 2019, 03:45
it was about the total points in first 4 and all 12 tests

So I calculated total points for first 4 and all 12 tests

But this is also not matching the OA .

We need OE for correct understanding

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Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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01 Apr 2019, 00:51
1
chetan2u

could you help here ....
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Joined: 19 Feb 2019
Posts: 10
Concentration: Marketing, Statistics
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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21 Apr 2019, 18:59
Hi can someone please explain how the answer is C and not D?
Senior Manager
Status: Gathering chakra
Joined: 05 Feb 2018
Posts: 251
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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25 Apr 2019, 20:44
Should be D, fixed it.

Assume the student got 100 on every test, then first four tests is 400 out of a total of 1200
400/1200 = 1/3
Re: A student took 12 tests. The student's average (arithmetic mean) on   [#permalink] 25 Apr 2019, 20:44
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