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Question 33 - Help please :)

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by aparna312 » Sat Nov 15, 2008 9:13 pm
I'm not getting the right answer. I'm sure I'm missing something basic here but please help:

A teacher gave the same test to three history classes: A, B, and C. The average (arithmetic mean) scores for the three classes were 65, 80, and 77 respectively. The ratio of the numbers of students in each class who took the test was 4 to 6 to 5, respectively. What was the average score for the three classes combined?

A. 74
B. 75
C. 76
D. 77
E. 78

** Answer: B. 75 **
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Re: Question 33 - Help please :)

by iamcste » Sat Nov 15, 2008 9:20 pm
aparna312 wrote:I'm not getting the right answer. I'm sure I'm missing something basic here but please help:

A teacher gave the same test to three history classes: A, B, and C. The average (arithmetic mean) scores for the three classes were 65, 80, and 77 respectively. The ratio of the numbers of students in each class who took the test was 4 to 6 to 5, respectively. What was the average score for the three classes combined?

A. 74
B. 75
C. 76
D. 77
E. 78

** Answer: B. 75 **

Avg=((65*4)+(80*6)+(77*5))/(4+6+5)=75
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Re: Question 33 - Help please :)

by iamcste » Sat Nov 15, 2008 9:21 pm
iamcste wrote:
aparna312 wrote:I'm not getting the right answer. I'm sure I'm missing something basic here but please help:

A teacher gave the same test to three history classes: A, B, and C. The average (arithmetic mean) scores for the three classes were 65, 80, and 77 respectively. The ratio of the numbers of students in each class who took the test was 4 to 6 to 5, respectively. What was the average score for the three classes combined?

A. 74
B. 75
C. 76
D. 77
E. 78

** Answer: B. 75 **

Avg=((65*4)+(80*6)+(77*5))/(4+6+5)=75

Avg=sum(n items)=n

Class A: we know the Avg and no of students hence we can get total marks of all the students

similarly for other classes

and use Avg forumala
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by aparna312 » Sat Nov 15, 2008 9:32 pm
Hey... Thanks a ton. Appreciate the swift response.

Guess that proves it.... my math is deplorable :)
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by EricLien9122 » Sat Nov 15, 2008 11:32 pm
just curious, what's the source of this question? I always thought the actual GMAT would have easier number for weighted average calculation.
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by stop@800 » Sun Nov 16, 2008 2:15 am
EricLien9122 wrote:just curious, what's the source of this question? I always thought the actual GMAT would have easier number for weighted average calculation.
As per gmat these calculations are easier....
65 * 4 = 260
80 * 6 = 480
77 * 5 = 385

can be done without paper pencil....
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by aparna312 » Sun Nov 16, 2008 11:32 am
Hey,

Its not that complicated (a regular prob I guess)... I was just being a lil obtuse :)

Its just from a set of test papers I got from a friend - don't know if its from any book bu the problems are quite interesting.
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