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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
Posts: 25
Concentration: Operations, General Management
WE: Engineering (Energy and Utilities)
In Sam’s chemistry class, his final grade consists of lab wo  [#permalink]

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06 Jun 2014, 00:36
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75% (01:47) correct 25% (02:43) wrong based on 207 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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Posts: 1834
Location: India
Concentration: General Management, Technology
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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, 01:19
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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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Joined: 25 Apr 2012
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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, 01:31
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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 2326 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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Re: In Sam’s chemistry class, his final grade consists of lab wo  [#permalink]

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06 Jun 2014, 02:34
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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In Sam’s chemistry class, his final grade consists of lab wo  [#permalink]

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22 Aug 2015, 22:20
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 1617 times ]

Senior Manager
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Posts: 457
Location: India
Re: In Sam’s chemistry class, his final grade consists of lab wo  [#permalink]

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20 Mar 2017, 03:35
1
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%
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Re: In Sam’s chemistry class, his final grade consists of lab wo  [#permalink]

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03 May 2018, 10:44
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%

Sam’s lab score of 80 counts as 2/3 of his grade, and his final exam score counts as 1/3 of his final grade. Letting his final exam grade = n, we can create the equation:

(2/3) x 80 + (1/3) x n = 75

Multiplying the equation by 3, we have:

2 x 80 + n = 225

160 + n = 225

n = 65

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Re: In Sam’s chemistry class, his final grade consists of lab wo &nbs [#permalink] 03 May 2018, 10:44
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