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

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Manager
Status: Gathering chakra
Joined: 05 Feb 2018
Posts: 182
A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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26 Mar 2019, 11:51
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0% (00:00) correct 100% (01:53) wrong based on 16 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) $$\frac{3}{8}$$
Intern
Joined: 18 Jan 2019
Posts: 27
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
Manager
Joined: 25 Feb 2019
Posts: 188
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
Intern
Joined: 18 Jan 2019
Posts: 27
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
Manager
Joined: 25 Feb 2019
Posts: 188
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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Manager
Joined: 25 Feb 2019
Posts: 188
Re: A student took 12 tests. The student's average (arithmetic mean) on  [#permalink]

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01 Apr 2019, 00:51
chetan2u

could you help here ....
Re: A student took 12 tests. The student's average (arithmetic mean) on   [#permalink] 01 Apr 2019, 00:51
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