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In the sample of 15 numbers, median will be (7th + 8th)/2, in this case 7th number is 1 and 8th number is 2 so median = 1.5

Average of the number is addition of all the numbers of defects divided by 15 = 3/5,

so Median - avg = 9/10, which lies between 0 and 0.5

Amar

I did it the same way, but, and Im sure Im being a moron, why if there are an odd number of mirrors do we need to average two items - surely the 8th mirror is the median?

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In the sample of 15 numbers, median will be (7th + 8th)/2, in this case 7th number is 1 and 8th number is 2 so median = 1.5

Average of the number is addition of all the numbers of defects divided by 15 = 3/5,

so Median - avg = 9/10, which lies between 0 and 0.5

Amar

Whoah there tiger. Median of 15 terms is the 8th term, not the average of 7th and 8th. Median is 2.

Mean of any set which consists of n odd integers is Quotient (n/2) + 1 = 15/2 + 1 = 8th term Mean of any set which consists of n even integers is the average of the "n"th and "n+1" term

For any arithmetic progression, Mean = Median = Average = Average of first and last term

Back to the problem.............. Average = 22/15, which is a little bit less than 1.5 (Why ? Because 1.5 x 1.5 = 225. Knowledge of squares comes in handy here. The GMAT never asks you to do busy work. Always remember that !!! ) Difference = 2 - (a term that is a little bit less than 1.5) = A term that is a little bit more than 0.5 Answer - c
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Median is 2 (take the middle number in the frequency) The average is 22/15 which you do not have to calculate just state that it is less than 1.5 (logic because 22.5/15=1.5)! Lets say 1.4 to make the logic simplier.

Therefore, you have the difference 2-1.4: 0.6.

The difference is between 0.5 and 1. Answer C.
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