Bunuel wrote:
On a certain math exam, 10% of the students got 70 points, 25% got 80 points, 20% got 85 points, 15% got 90 points, and the rest got 95 points. What is the difference between the mean and the median score on this exam?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
We can let the number of students = 100, thus:
10 had a 70
25 had an 80
20 had an 85
15 had a 90
30 had a 95
The median position is (100 + 1)/2 = 50.5, i.e., the average of the 50th and 51st numbers. We see that they both are 85, so the median is also 85.
The mean is:
(10 x 70 + 25 x 80 + 20 x 85 + 15 x 90 + 30 x 95)/100
(700 + 2000 + 1700 + 1350 + 2850)/100
8600/100
86
So the difference between the mean and the median is 86 - 85 = 1.
Answer: B
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77% (02:50) correct 
