OG The average score on a test taken by 10 students

AbeNeedsAnswers wrote:The average (arithmetic mean) score on a test taken by 10 students was x. If the average score for 5 of the students was 8, what was the average score, in terms of x, for the remaining 5 students who took the test?

A) 2x – 8
B) x – 4
C) 8 – 2x
D) 16 – x
E) 8 – (2/x)

A

Total score of all the 10 students = Total score of the first batch of 5 students + Total score of the second batch of 5 students

We have,

Total score of all the 10 students = 10*x = 10x;
Total score of the first batch of 5 students = 5*8 = 40;

Thus,
Total score of the second batch of 5 students = 10x – 40 = 10(x – 4);

Thus, the average score of the second batch of 5 students = 10(x – 4) / 5 = 2(x – 4) = [spoiler]2x – 8[/spoiler].

The correct answer: A

Hope this helps!

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Hi AbeNeedsAnswers,

This question can be solved by TESTing VALUES.

We're told that average score on a test taken by 10 students = X and that the average score for 5 of those students was 8. We're asked for the average score of the OTHER 5 students.

IF... X = 10, then the TOTAL points for ALL 10 students = (10)(10) = 100
Since 5 of those students averaged 8 points, that accounts for (5)(8) = 40 of those 100 points.
This leaves 100 - 40 = 60 points for the remaining 5 students, which is an average of 60/5 = 12.

So we're looking for an answer that equals 12 when X=10... There's only one answer that matches...

Final Answer: A

GMAT assassins aren't born, they're made,
Rich

The two groups are equal in size (5 students each), so the overall average score will just be the ordinary average of the scores of each group, because each group is equally important. If x is the average of two things, then 2x is the sum of those two things. So if y is the average we want to find,

y + 8 = 2x
y = 2x - 8