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# Each student in a certain class is considered intermediate or strong,

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GMATH Teacher
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Each student in a certain class is considered intermediate or strong,  [#permalink]

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19 Feb 2019, 14:13
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Difficulty:

15% (low)

Question Stats:

79% (02:18) correct 21% (02:56) wrong based on 28 sessions

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GMATH practice exercise (Quant Class 6)

Each student in a certain class is considered intermediate or strong, but not both. The average of the grades of the strong students is 6.3 points, exactly two points above the average of the grades of the intermediate students. What is the percentage of strong students in this class, if the average of all students grades in this class is half point below the average of the grades of the strong students?

(A) 60%
(B) 65%
(C) 70%
(D) 75%
(E) 80%

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Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

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Re: Each student in a certain class is considered intermediate or strong,  [#permalink]

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19 Feb 2019, 14:24
AV of strong students = 6.3
AV of intermediate students = 4.3 (given)
AV of all students = 5.8 (given)
Let number of strong students be s and number of intermediate ones be i.
(6.3s + 5.8i)/(s + i) = 5.8

Solving this gives s = 3i
So Answer = (3i/(3i+i))*100 = 75% = D

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GMATH Teacher
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Re: Each student in a certain class is considered intermediate or strong,  [#permalink]

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20 Feb 2019, 11:40
fskilnik wrote:
GMATH practice exercise (Quant Class 6)

Each student in a certain class is considered intermediate or strong, but not both. The average of the grades of the strong students is 6.3 points, exactly two points above the average of the grades of the intermediate students. What is the percentage of strong students in this class, if the average of all students grades in this class is half point below the average of the grades of the strong students?

(A) 60%
(B) 65%
(C) 70%
(D) 75%
(E) 80%

$$?\,\, = \,\,{{100} \over {100 + x}}$$

$$\left( {{\text{Alligation}}} \right)\,\,\,\,?\,\, = \,\,\frac{{100}}{{100 + x}}\,\, = \,\,\frac{{5.8 - 4.3}}{{6.3 - 4.3}}\,\, = \,\,\frac{{1.5}}{2}\,\, = \,\,\underleftrightarrow {\frac{1}{{10}}\left( {\frac{{15}}{2}} \right) = 0.75}\,\, = \,\,75\%$$

We follow the notations and rationale taught in the GMATH method.

Regards,
Fabio.
_________________

Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

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Each student in a certain class is considered intermediate or strong,  [#permalink]

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Updated on: 20 Feb 2019, 11:59
I = 4.3 and Strong = 6.3
avg of class = 6.3-0.5 ; 5.8
so we can say
x*43+6.3*y/x+y= 5.8
we get
3x=y

to find
y/x+y
so
3x/4x = 75 %
IMO D

fskilnik wrote:
fskilnik wrote:
GMATH practice exercise (Quant Class 6)

Each student in a certain class is considered intermediate or strong, but not both. The average of the grades of the strong students is 6.3 points, exactly two points above the average of the grades of the intermediate students. What is the percentage of strong students in this class, if the average of all students grades in this class is half point below the average of the grades of the strong students?

(A) 60%
(B) 65%
(C) 70%
(D) 75%
(E) 80%

$$?\,\, = \,\,{{100} \over {100 + x}}$$

$$\left( {{\text{Alligation}}} \right)\,\,\,\,?\,\, = \,\,\frac{{100}}{{100 + x}}\,\, = \,\,\frac{{5.8 - 4.3}}{{6.3 - 4.3}}\,\, = \,\,\frac{{1.5}}{2}\,\, = \,\,\underleftrightarrow {\frac{1}{{10}}\left( {\frac{{15}}{2}} \right) = 0.75}\,\, = \,\,75\%$$

We follow the notations and rationale taught in the GMATH method.

Regards,
Fabio.

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Originally posted by Archit3110 on 20 Feb 2019, 11:49.
Last edited by Archit3110 on 20 Feb 2019, 11:59, edited 1 time in total.
GMATH Teacher
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Posts: 905
Re: Each student in a certain class is considered intermediate or strong,  [#permalink]

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20 Feb 2019, 11:54
Archit3110 wrote:
fskilnik
how did you deduce value of 5.8?

Hi Archit3110 !

"... the average of all students grades in this class is half point below the average of the grades of the strong students"

Hence: 6.3 - 0.5 = 5.8

Regards,
Fabio.
_________________

Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

Re: Each student in a certain class is considered intermediate or strong,   [#permalink] 20 Feb 2019, 11:54
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