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# In Sam’s chemistry class, his final grade consists of lab wo

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Intern
Joined: 24 May 2013
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Concentration: Operations, General Management
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In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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05 Jun 2014, 23:36
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Question Stats:

73% (01:57) correct 27% (02:31) wrong based on 172 sessions

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In Sam’s chemistry class, his final grade consists of lab work and the final exam. If lab work is 2/3 of the final grade, and he scores 80%, what must he score on the final exam to earn a final grade of 75%?

A. 65%
B. 68%
C. 70%
D. 73%
E. 75%
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Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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06 Jun 2014, 00:19
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Answer = A = 65%

Let the total final marks (Lab + Exam) = 300 (Out of marks)

Lab is $$\frac{2}{3}$$ rd, so exam would be $$\frac{1}{3}$$rd

Setting up the table as below

Lab .............. Exam ................. Final

200 ................ 100 ...................... 300 (This are the max. marks for which exam is conducted)

Has got 80% in Lab & requires 75% in final

80% of 200 = 160; 75% of 300 = 225

160 ................. x ............................ 225

So marks required in Exam (x)

= 225 - 160

= 65%
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Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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06 Jun 2014, 00:31
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nidhi12 wrote:
In Sam’s chemistry class, his final grade consists of lab work and the final exam. If lab work is 2/3 of the final grade, and he scores 80%, what must he score on the final exam to earn a final grade of 75%?

1. 65%

2. 68%

3. 70%

4. 73%

5. 75%

Sol: If you are good with weighted average concept then it shouldn't take you long

Here is how I would approach this problem.
Attachment:

Untitled.png [ 6.65 KiB | Viewed 1857 times ]

It is given that Lab work exam has 2/3 weightage and final exam therefore will have weightage of 1/3
Therefore by weighted average ratio.

The final grade score of 75% will be twice as close to Lab exam average then final exam average

Now If total distance between Final exam and Lab exam is x
then x/3 will be distance between Lab exam score and Total final grade score and
2x/3 will be distance between final exam score and Total final grade score

Given x/3 =5 so x= 15

and therefore 2x/3 =10. So Final exam score will be 10 less than grade score of percentage of 75 ie. 75-10= 65%

Ans is A.

Another way to do it will be

$$\frac{W1}{W2}$$= $$\frac{(A2- Avg)}{(Avg- A1)}$$

W1=1/3
W2=2/3

So W1/W2= 1/2
$$\frac{1}{2}$$ = $$\frac{(80-75)}{(75-x)}$$

1/2 = 5/(75-x)

75-x=10 or x =65%

For more on weighted average concept..Check out Veritas prep blog:

http://www.veritasprep.com/blog/2011/04 ... ge-brutes/
http://www.veritasprep.com/blog/2011/03 ... -averages/
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Posts: 43900
Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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06 Jun 2014, 01:34
nidhi12 wrote:
In Sam’s chemistry class, his final grade consists of lab work and the final exam. If lab work is 2/3 of the final grade, and he scores 80%, what must he score on the final exam to earn a final grade of 75%?

A. 65%
B. 68%
C. 70%
D. 73%
E. 75%

Similar question to practice: a-student-s-average-arithmetic-mean-test-score-on-4-tests-137873.html
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Posts: 13758
Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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22 Aug 2015, 18:40
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In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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22 Aug 2015, 21:20
This problem can be solved quickly and accurately by "Allegation method"
The wights are in proportion of 2/3:1/3 i.e, 2:1. The same is maintained in below sketch.
X must be (75-x) = 10. Hence X=65
Attachments

1.JPG [ 2.91 KiB | Viewed 1150 times ]

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Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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19 Mar 2017, 06:30
Hello from the GMAT Club BumpBot!

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Re: In Sam’s chemistry class, his final grade consists of lab wo [#permalink]

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20 Mar 2017, 02:35
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nidhi12 wrote:
In Sam’s chemistry class, his final grade consists of lab work and the final exam. If lab work is 2/3 of the final grade, and he scores 80%, what must he score on the final exam to earn a final grade of 75%?

A. 65%
B. 68%
C. 70%
D. 73%
E. 75%

2/3 * 80 + 1/3 *x = 75
x = 65%
Re: In Sam’s chemistry class, his final grade consists of lab wo   [#permalink] 20 Mar 2017, 02:35
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# In Sam’s chemistry class, his final grade consists of lab wo

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